Do you guys lock your elbows when doing any kind of raises?

I asked this question on the workout board but I figured maybe it would be better be placed here:

Do you guys lock your elbows when doing any kind of raises?

I always thought that you should never lock your elbows and always keep them a little bent when doing either front, scaption, side, or bent over raises. But one of my physical therapists said you should keep your elbows locked when you do front raises so you completely isolate the front delt (I never asked them about scaption, side, and bent over raises). What do you guys think? I've read numerous articles on the net saying to never lock your elbows and to always keep them a little bent but the articles never go into detail why. Is there a medical reason why you shouldn't lock your elbows or is it that keeping them a little bent hits the muscle better?

Any and all views would be greatly appreciated.