1. It is very hard to pin down who is responsible for anything.
2. You end up explaining everything twice - once to your front wo/man contact and then again to the clueless intern who is tasked with implementing what you want.
3. It is near impossible to determine the competency of the person who will be doing the work in advance. The front person is usually quite good, but the person who actually does the work is often not. You can’t work that out until you are well into the project.
Teams on average are probably better than individuals, but from a project management perspective they are a pain to deal with.