I recall a few UFC shows ago, Ivan Menjivar did an interview with MMAFighting where he wished that weigh ins were day of. He remarked that if that were the case, he would be fighting at Welterweight! Interesting. A guy that normally sweats himself down to 135 would naturally be fighting at 170.
If the weigh ins were moved to the morning of the fight, what do you think would be the effect? I think at a minimum, as competitive as MMA is, fighter's would be forced to take nutrition and health a lot more seriously. I think there still would be guys sweating off the pounds and then rehydrating to gain more weight advantage, but that margin of fighter weight difference would be reduced significantly. I am speculating that with day of weigh-ins, gone are the days of fighters weighing in at two or more classes above their weight class when fight day rolls around. So a guy like Gleison Tibau would probably fight at Welterweight, and not Lightweight.