Yesterday I overhead a man at a dive shop. He was complaining to his wife that he felt he was carrying too much weight on his dives. In his words, "I'm overweighted for the beginning of my dive, but if I carry less I'll balloon to the surface near the end of my dive. I start to feel it when I'm down to about 1200 PSI."
I say he's not overweighted, but rather weighted just right. If you remember how to do a proper buoyancy check, you'll recall that you do it with a near empty tank. Your weights should be able to keep you underwater with an empty cylinder.
Weights have two purposes: to get you underwater at the beginning of the dive and to keep you underwater until the end, when you decide it's time to come up. The correct weighting is the smallest amount that satisfies these requirements---something this guy forgot.