everyone cuts, but just because you can make a weight doesn't mean that it is your best weight. It isn't as simple as making weight and then putting 20 pounds on overnight. If someone is cutting that much it should be done over the course of several weeks, which takes lots of effort and it is very taxing on the body. Sometimes a fighter can be better if they are on full feed at a higher weight.
That being said, most people are well served by fighting at the lowest possible wieght. Not everyone, however.