One thing for sure we won't have Chavez Jr. campaigning at 160. Rios would of never been at 135. Broner would of never been at 130. It would make the sport more honest as far as having fighters fight at a more natural weight
The WBC said about half a year ago they would return to same day weigh-ins in July, only they never did and completely ignored the issue further. It makes a lot of sense to return to the old format, because it's a lot fairer.
Pro : No more fighters picking on smaller guys Con : Cash cows would have to fight guys their own size. Promoters and sanctioning bodies won't let that happen.
There needs to be year round weighing to make sure the fighters are fighting at their natural weights and not gaming the system putting their own health at risk. Perhaps something like be within 5% of your fight weight at any time.
I think the main reason they weight in a day before is to have two days to build the event and provide time in handling weight issues. This is probably a marketing decision. To my naked eyes the welter weights of the 50's do look like light weights of today.
It needs to be done, unfortunately it won't. A lot of weight drained fighters have serious liver and organ problems later on life. You would also get fairer size matchups for the fight. I think it benefits more conditioned fighters as well. If you have to drop 10 pounds the day of the fight you're going to get tired fast, whereas if you have a 30 hour rehydration period then it wouldn't really bother you the next day. It promotes the event the day before and used as a public relations thing the day before. I doubt promoters would ever want to go back to same day weigh ins.
Id hate to rain on anyones parade,but theres a reason weigh ins are now a day before the fight. Guys used to always starve and drain themselves to make weight, they'd just end up putting on 10lbs in 12 hours rather than 36. It was very unhealthy. The current system allows guys to safely re-hydrate
During the days of same day weigh ins, fighters would sometimes be weak when they entered the ring. This way, we know fighters will be at full strength. Of course, some have manipulated the system to gain extreme advantages. Plus, like bluebottle pointed out, the Friday weigh ins are promotional tools. They generate buzz and PPV buys. We aren't going to see this change.
Same day weigh-ins was abandoned after the Mancini-Kim disaster and following the cancellation of the Spinks-Muhammad rematch.
The pros outweigh the cons in this case, but the biggest con as I see it is that you will still have some crazy fighters that will cut weight ridiculously and step into the ring anyway without gaining much back if the fight is important enough.