How do soldiers change the roles of their equipment as the battlefield changes?

Lets say that you have a 4X ACOG scope on your rifle with an Aimpoint Red dot and the enemy moves in within 30 yards. Do soldiers usually quickly remove the scope since you would not need it? Is it practical to take it off during a firefight? Or if you are on a mission shooting at some range with a 12x scope on a .308 AR 10 would you then carry something else just in case the situation changed into a close in battle? Im just wondering how they change roles in a combat situation. Thanks!