First, good diffusion costs a lot more than good absorption. So the very first consideration is your budget. If you need to do this cheaply then forget diffusion. But if you're aiming high, then diffusion can be useful in both a tracking room and a control room.
In both cases absorption or diffusion can reduce flutter echo and make a room sound larger than it is. Two places where you definitely want absorption and not diffusion are at the side-wall and ceiling reflection points in a control room, and on a low ceiling above a drum set or anywhere else you'll use overhead microphones.