Besides the diversion of a great deal of German combat power from other theaters, the operations in the MTO had two other effects which were vital for the success of later Allied operations in Europe:

1. It allowed the U.S. forces to get "blooded" and work out the kinks in their operational methodology, which to that point had been purely theoretical for all those personnel, from the lowest private all the way up to Patton and Bradley. None of them had ever before fought in a war conducted on modern (for WWII) principles, with mobility and flexibility. Some had fought in the Pacific, but that was a completely different kind of warfare with different requirements and lessons.

2. It allowed U.S. and U.K. forces to work out and perfect methods of interoperability, particularly between varying branches of their respective armed forces. For example, American planes flying combat support missions for British troops, and vice-versa, needed to work out methods and mechanics of communications so that incidents like the relatively high friendly fire casualty rate of Anzio would not plague the far more large scale and complex D-Day and post-D-Day operations.