You are either fucking with me or you are a complete moron or both.... Hell I may be the moron for even debating with you.
The weight classes are intended to level the playing field and pit like-sized guys against each other. The "advantage" fighters attempt to gain in CUTTING weight is to try to fit into a smaller weight class in order to fight smaller opponents.
Maybe this helps: let's say you have an ass-kicking competition and you set the divisions up by shoe size. I wear a size 13-14 but if I could, somehow, squeeze my floppy, flat foot into a size 10 shoe for 5 minutes at "weigh-ins", my kicks would have more impact and mass than a guy who really wears a size 10 shoe. I would try and do everything in my power to get my foot into that shoe and avoid opponents in the 13-14 sized shoe range. However, I would make sure to try to act "real cool" so that I, too, could have moronic fans defending me and saying that I am a natural size 10 because I can fit into the shoe for 5 minutes 24 hours before the competition starts.
Do you understand, now???