Most guys will cut down a bit. GSP tends to stay at 185 now. Cutting is very rough on your body. Anybody who has dieted knows how brutal it can be, now imagine it but compressed in a much shorter amount of time. GSP stays close to fighting weight to prolong his career.
Alves tends to be an exception, because he fought in 100 at about 195lbs but thats what hes known for. Other guys i tend to think of is Sean sherk who i have NO IDEA how he makes lightweight. usually its the wrestlers who are used to making big cuts, 10-20 lbs of water weight.
Others like spider silva and a lot of strikers and japanese fighters tend to only lose about 5 lbs.
You usually spend 2-1 week prepping for the cut, you take out all salt or anything that makes your body retatin water out of your diet. then hit a target weight where you know you can make a cut easily. Alves got off the plane at 182-188 lbs usually when he fights other guys get it closer Rich franklin hits vegas at 10 lbs over which is about right. then they sweat off basicly 5 litres of water, lots of cardio and sauna if needed.
Another factor is the size of the guys, the bigger the body easier to drop water weight, much harder for a light weight to lose 10lbs then a heavy weight. A lot of heavy weights like brock will lose 15lbs over a few hours of training. I lose about 5 lbs over a 2 hour intense training period and im at fighting weight of 160.
edit: all weight in's i personally know of are the day/morning before. Only one i know that weights in twice personally is OFSAA for Ontario championships for wrestling. you weight in day before and morning of.