You often hear the UFC commentators talking about XYZ fighter who's gone through a severe cut before the fight, and the detrimental effect this may have on his health and performance.
If I was one of those fighters I'd be working out what weight I wanted to fight at over the medium term and gradually get my body composition to the point where I only need to cut a couple of kgs before a fight, rather than this 8-10kg bullshit. That can't be good for you...the body needs to adjust gradually.
I agree with Andy's comment re skill > strength for a fighter. Strength is obviously a good advantage, but it's nothing without the skill. Anderson Silva is the best MMA fighter going around ATM, but he'd hardly rate a mention if you're talking about the strongest fighters. The guy is just all skill.