The origin of day before weigh in's goes back to when boxing became a big media event in the late 60's, early 70's. Ali was a big part of it. Before that boxers were not only weighed in the "day of" but most were weighed in hours or minutes before the fight. But someone finally figured out, "hey, let's get these guys together the day BEFORE the fight, have them weigh in, do a little press conference, let them talk some smack, and we'll generate even MORE interest in this fight!" But, here's the rub. Back then no one cut. Everyone trained, got into shape, and fought in whatever weight class they NATURALLY belonged in. Not a single fighter bitched and whined about it. Why? Because they all fought at their natural weight anyway. It took a full decade or so before some boxers in the smaller weight classes finally said, "hmm, you know what? I could weigh in on Friday and then add a couple pounds before my fight on Saturday. That might give me an advantage?" Again, it was only a COUPLE of pounds "back in the day." Now fast forward to 2005. The advances in sports medicine and our knowledge of physiology has grown tremendously. Now we have people like Billy Rush who can help a fighter "weigh in" at one weight but actually get him ready to fight 20, 25, even 30 pounds heavier the next day. Technically this may all be "legal" (for all those of you who say it isn't cheating) but the fact is that they are still "gaming the system." I still don't understand how you can have a UFC Welterweight Title match...between 2 guys who enter the Octagon at 190lbs.? (see: GSP vs. Hughes.) Another one that burns me is when Riggs fought Hughes. Hughes weighed in, made 170 and sat down. Immediately began drinking his pedialyte and had a sandwich, power bars, etc. Riggs didn't make weight. Went away to cut. Came back and STILL didn't make weight. Weighed in at 173 I think? The rub? Hughes was sitting right there next to him and actually weighed MORE than Riggs did right at that moment. So what's so special about the weigh in? We have weight classes to try and ensure even matches between competitors who supposedly belong to that weight class. Why the day before? Why not a week before? Hell, I weighed 170 in High School, why can't I take that weight?
Weight classes are there for a reason. "Allowing" fighters to cut defies that reasoning.