As you might know, the writers' strike forced Bay to start work on TF2 without an actual script — all he had was an outline by writers Roberto Orci and Alex Kurtzman. So a lot of the movie's early designs and ideas came about without a real script, and when Orci and Kurtzman came back to work after the strike, Bay was able to tell them which robots he wanted in the movie. As he says in this clip, all of that pre-visualization work and brainstorming with artists actually informed the movie's script, once it finally had one. You probably have your own ideas about whether that was a good thing.
Transformers: Revenge Of The Fallen comes out on DVD tomorrow, October 20, on Blu-Ray and DVD, wherever awesomeness is available.