The current NBA has big men at a premium, so once you get your hands on one, you should do all you can to retain him. That is exactly what Chris Kaman is.
A guy that can score with either hand on the low block, has a decent jumper for a big man and plays good defense. Kaman's contract has three years and $44 million left on his deal, not quite a bargain, but also not overpaying.
So, why would the Clippers want to deal a relatively young center? Simply for the fact that they have an overload up front and need to open up playing time for young players like Blake Griffin and DeAndre Jordan.