Why would clients pursue tax recovery if they can write-off withheld taxes on their tax returns?

The IRS prohibits taxpayers from claiming over-withheld taxes as a foreign tax credit if recourse is available through a foreign tax treaty. The IRS website states: “The amount of foreign tax that qualifies as a foreign tax credit is not necessarily the amount of tax withheld by the foreign country. If you are entitled to a reduced rate of foreign tax based on an income tax treaty between the United States and a foreign country, only that reduced tax qualifies for the credit. It is up to you whether you want to ask for a refund from the foreign country of the difference (excess) for which a foreign tax credit is not allowed.”