There is no clearcut answer. It depends on the intended functionality of the assy. In some cases it may be important but not in others.
As Jeff said, it all depends on who the target audience is for the drawing. If they are interested in how far the fan can turn from side to side, then add the dimension. If they don't care how much travel the buttons have or how far they might stick out, then leave that dimension off. If you put on too many dimensions, people will complain that it is confusing. If you put on too few, they will compain that it doesn't give them what they need. If you get it right, no one will notice and on one will thank you.