Note: in this trade Mark Blount signifies the expiring contract of Quentin Richardson
Why they do it?
Heat: They need a low post PF & scorer. If Boozer works out they keep him, if not they still have 2010 flexibility. Thomas is an expirer, who is added depth. Plus, they'd love to add to the fun of Q Rich traded for the 5th time.
Jazz: This is about as close to equal value as it gets. Garcia would probably start over Miles @ SF, he's a solid shooter, and okay defender. Then Miles can come off the bench to replace Harpring who looks to be retiring. Haslem is a Jerry Sloan type of player. He'll provide defense, hustle, he knows the pick & roll very well, and won't cause any problems.
Kings: They are also recieving a conditional first rounder from Miami (whichever is lower of their two 2010 picks). They are saving around $4.5M right away because of BYC of Garcia, and more money for years to come. They made a terrible mistake signing Udrih to that deal, and will need to move Garcia to free up cap for the future. They already have Nocioni who is a better fit at SF anyway, and the draft pick Casspi can develop as his backup. Q-Rich can also do alot of the things Garcia did.