It would simply change the no-braining from LMGs to close combat weapons. If LMGs had a set up time you would pretty much auto-win every engagement against them with close combat troops.
Meet an LMG squad that is moving out in the open? You will be in close combat range before he gets a change to fire his LMG.
Meet an LMG squad standing still in cover? Throw a grenade, force them to move -> LMG is now useless while you close in.
Not necessarily setup time. Just a cooldown after rotating and we're done, voila. By coming close and keeping moving you can micro your way to victory in the engagement.