Following our last post, where Mike shared how two clients (his now-famous “London buses”) asked the exact same question about in-house tax expertise, one thing quickly became clear to me: the conversation does not stop at, “Should we do this?”.

In this blog post, we’re exploring the next question:

What are the real pros and cons?

At first glance, the role of an in-house Mobility Tax Advisor can sound like an obvious win. However, the reality we see with clients is more nuanced. Some programs genuinely unlock significant value, while others struggle to justify the investment. Most mobility programs sit somewhere in between.

So, rather than trying to land on a simple yes-or-no answer, let’s look at what we’re consistently hearing from mobility leaders.

Where does this role really add value? And where do the challenges tend to show up?

As highlighted in the previous post, large, complex programs often benefit the most from building in-house tax expertise. But as mobility programs evolve, many organizations are weighing this option against continued reliance on external providers.

While the potential value is clear, the decision is rarely one-size-fits-all. It depends on a range of factors, from company culture and mobility strategy to program complexity and policy design.

With that in mind, below is a practical breakdown of the key pros and cons, based on what we’re seeing in the market today, to help guide your thinking.

Where an In-House Mobility Tax Advisor Delivers the Most Value

Rather than thinking about the benefits in isolation, the real question we hear from Mobility leaders is:

“Where does this actually make a meaningful difference in my program?”

The value of an in-house tax advisor tends to show up differently depending on the scale, complexity, and operating model of your mobility program.
Here’s how that plays out in practice:

1. For Large, Complex Programs: Unlocking Scale and Cost Control

For organizations with high volumes, multiple assignment types, and global footprints, this is often where the role delivers the most immediate and measurable value.

In these environments, an in-house advisor can:

  • Act as a central control point across hundreds of cases

  • Reduce fragmented communication with tax partners

  • Drive consistency in how tax is applied across regions and policies

  • Identify cost leakage at scale (e.g., TEQ, shadow payroll gaps, redundant services)

Why it matters:

At scale, even small inefficiencies multiply quickly. This role helps standardize decisions (tax approach, payroll set up, TEQ policy) and control costs across the entire program, not just on individual cases.

2. For Programs with High External Spend: Rebalancing the Cost Model

If your program relies heavily on external tax providers, an internal advisor becomes a lever to reshape costs, not just reduce.

They help:

  • Filter and prioritize what truly needs external advisory

  • Reduce iterative back-and-forth with providers

  • Challenge and validate external advice where appropriate

  • Support smarter scoping of services

What we see in practice:

Organizations don’t eliminate tax partners but instead they use them more selectively and strategically, often reducing unnecessary spend while improving outcomes.

3. For Evolving or Less Standardized Programs: Enabling Better Decision-Making

Programs that benefit significantly from inhouse tax expertise during decision-making and assignment planning include:

  • Expanding into new regions

  • Moving beyond traditional assignment types

  • Programs dealing with frequent exceptions

An in-house advisor can:

  • Advise in real time on different structuring options

  • Help the business understand trade-offs (cost vs. experience vs. compliance)

  • Move decisions upstream—before tax becomes an issue

4. For Programs Struggling with TEQ or Cost Recovery: Driving Financial Discipline

This is one of the most underappreciated but high-impact areas.

Where organizations have:

  • Aging TEQ balances

  • Low tax payment recovery rates

  • Ongoing employee disputes

…the presence of an internal advisor can significantly tighten processes.

They can provide:

  • Ongoing oversight (not just year-end involvement)

  • Direct engagement with stakeholders and assignees

  • Internal accountability for collections and reconciliations

The outcome:

Less “leakage,” stronger controls, and measurable improvement in financial recovery over time.

5. For Cross-Functional Organizations: Bridging Structural Gaps

In companies where Mobility, Payroll, Finance, and Corporate Tax operate in silos, the biggest value is often organizational, not purely technical.

An in-house advisor becomes:

  • A translator across functions

  • A consistent voice in planning conversations

  • A connector between internal teams and external providers

Why this matters:

Many mobility challenges aren’t purely tax issues - they’re alignment issues.

This role helps eliminate friction that otherwise slows decisions or creates risk.

Where the Challenges Tend to Arise

Of course, as with most things in mobility, it’s not all straightforward. Here are some challenges where organizations may pause or hesitate to hire an in-house tax advisor.

⚠️ 1. Headcount and Budget Constraints

Even when the value is clear, making space for an additional role isn’t always easy.

There might be challenges around:

  • Justifying adding headcount to Mobility in cost-sensitive environments

  • Budget ownership sitting outside the function

  • Relocation (including external tax) costs are often passed through to the business unit which makes it more complex to allocate the cost of an in-house tax expert

Reality: The upfront cost can be a barrier, even with long-term savings.

⚠️ 2. Risk and Liability Considerations

Another common concern is how risk is perceived and managed.

  • With external providers, liability is clearly defined and often sits outside the organization
  • With internal expertise, there can be a greater sense of direct accountability

What this means in practice: Clear governance, role definition, and boundaries become even more important. 

⚠️ 3. Program Size and Complexity

This is one of the biggest determining factors. Not every program will benefit equally:

  • Smaller or highly standardized programs may not need a dedicated full-time resource
  • Lower volumes can make it harder to justify the investment

Simply Put:

The business case depends heavily on scale and complexity. The more complex and varied the program, the stronger the case tends to be.

⚠️ 4. Limited Jurisdictional Expertise

Even the most experienced in-house tax advisor won’t be an expert in every tax jurisdiction. Typically, Global Mobility tax roles are filled with tax professionals that often bring a background in Finance having worked for one of the Big 4 accounting firms.

That means:

  • External providers still play a critical role in ensuring global coverage and providing access to a strong global tax network
  • A balanced, hybrid approach works best, leveraging internal insight alongside external depth.

⚠️ 5. Internal Alignment and Cost Allocation Challenges

This is one of the more practical but often underestimated challenges.

Questions we hear frequently include:

  • Who “owns” the role? Global Mobility, Finance, or Corporate Tax?
  • How is the cost allocated?
  • How do we align priorities across functions?

From experience:

Getting this right early on makes a significant difference to long-term success.

Key Takeaway: It’s Not Either/Or

The most effective mobility programs don’t eliminate external providers. Instead, they optimize how they use them.

They take a balanced approach by:

  • Building internal capability where it adds the most value

  • Using external providers more selectively and strategically

  • Creating a more efficient and connected overall model

Final Thought

If there’s one thing that stands out from all these client conversations, it’s this:

There isn’t a single “right” answer.

The decision to bring tax expertise in-house really comes down to:

  • The complexity of your program

  • Your cost structure and current consulting spend

  • Your organization’s appetite for investment and risk

  • Your business culture

But when the conditions are right, this role can become much more than an additional resource. It can fundamentally change how mobility decisions are made and how effectively organisations deploy talent globally.

Contact Us

If you’re considering whether in-house tax expertise is right for your mobility program, AIRINC can help you assess the business case, evaluate your current provider model, and benchmark your approach against peer organizations. We can also help you identify the right balance of internal capability and external support to meet your organization’s cost, governance, and talent mobility goals.

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