Poster wasn't talking about swapping KT for a long term contract where the motivations there are obvious.
I think the point that the poster was making, and a sensible one, was why on Earth would a team trade their own expiring player, who can play, for our expirng player, who sucks?
Then of course someone had to race in and claim no! Kenny doesn't suck! Yes he does. And in comparison to a Boozer or whatnot he absolutely sucks.
In any case, that makes no sense unless a team is just over the luxury tax and looking to shed a million dollars or two. In any other situation you want to still have the guy who can play, Boozer or whoever. You can resign him, trade him for a valuable piece, sign and trade him, and you get a talented player for the remainder of the year.