A recent study looked at the financial cost to companies when they reduce or completely eliminate tax services performed by the firms that supply their auditors, and it found that such actions create a short-term spike in tax rates and payments, said CFO.com. The study looked specifically at firms that stopped using their audit firms to perform tax services in order to reduce suspicions from regulators about the reliability of their financial information.

The study found that in 419 instances of companies decoupling tax and audit services, the companies' effective tax rate went up by mean 1.36 percentage points in the following year, and their actual cash payments went up by 1.64 percentage points. On average, this translated into an average of $6.4 million in additional taxes per company in the amount owed, and about $7.65 million extra in what they paid. Losses were even higher among companies that got rid of auditors that specifically had tax expertise.

At least part of these additional costs came from the new firms sent to do their taxes, which weren't as familiar with the company and so were not as effective in coming up with tax avoidance strategies. This might explain why these tax increases were short-term, generally lasting about a year, as the tax practitioners gained more experience with the company.