Takeoff and descent in PROF mode is recommended actually. You just have to be more aware of what the airplane is doing as opposed to just "setting it and forgetting it". The crew must constantly monitor all phases of flight. As rudimentary as it is, the A300/A310 does better than the EMB-190 in real life. Typical rule of thumb for decent is that youll cross a constraint at the altitude you want, or speed, but not both. In either case, use the spoilers to get you where you need.