Look at The GOAT Roy Jones Jr once he went up from Light Heavyweight to Heavyweight he was never the same again when trying to go back down. Basically when you do it in a short period a time and up in age drastic weight loss affects your immune system. Not good for the body.
Well, the difference between Heavyweight and Light Heavyweight is 25 pounds though....to put that in perspective, it's the exact same difference in weight between Super Bantamweight and Welterweight, which is a 6 division jump. Manny Pacquiao would never be able to fight successfully at Super Bantamweight again just like Roy wasn't able to at Light Heavyweight.
Yes, fighters can go UP and come DOWN in weight depending on the actual pounds. Hank Lundy fights at 140 & 135, Dierry Jean does the same. Rances Barthelemy as well because it's only a 5 pound difference. Paul Williams fought at 147, 154, 160, and back to 154. Broner went from 130 to 135 to 147 to 140. Floyd was able to hold both the 147 & 154 titles, because it was only a 7lb difference between the divisions. We can go all day with this, but to the question which was raised, it depends on the divisions, age, & actual real pounds being lost. An older fighter can't bounce around in weight and still be successful amongst the elite the same way a younger fighter can.