I notice that many of the fighters in ufc cut about 5-20 pounds of weight before their fight, and when they're training, they intentionally gain some more weight while training. I don't really understand this.... wouldn't you want to train at the weight at which you're going to fight at, since its more 'realistic' and you will have a feel of what it will be like to fight at that weight?

sorry if I sound ignorant I only do muay thai I don't really know much about mma