Via Fred Kagan:

The group also ignores another inconvenient fact. Some of the most important training Iraqi Army units get today comes from operating side-by-side with American combat units in clear-and-hold missions, searches and raids. It is one thing to have trainers tell you what to do and watch you do it. It is another to participate in well-planned and skillfully-executed operations. Ironically, pulling American forces back from combat missions will actually remove one of the most important elements of training Iraqi forces.