The 3 teams being the Blazers, the Mavs & the Clippers. Here it is:
Why they would do it, team by team:
Portland: The Blazers absorb the ugly but not horrific contract of Ryan Gomes and in the process pick up a nice young piece in Rodrigue Beaubois. They limit their cap options for the summer to a degree which is a downside.
Dallas: Dallas desperately needs to move Shawn Marion and only a contending team would be willing to pay 27 million over the next 3 for him. he's good and he helps now but by moving him and amnestying brendan haywood, dallas can now offer 2 max contracts ( i think - roughly 16 mil per year each in the 1st year ) to deron williams & dwight howard. they pretty much take themselves out of contention for this year but when they chose not to resign tyson chandler, it was clear they were angling for a big move this summer. This deal allows them to do it. Beaubois is a nice piece but if they get williams, his minutes would be more limited anyway. Felton & Cook give them some minutes down the stretch to reduce dirk and potentially kidd's minutes ( assuming kidd can come back for one more run )
LA Clippers: The Clippers get the 2 guard they need and pick up a excellent wing defender for their playoff run. Sure they now have too many wings but given their weakness is defense, they may be better off playing more shawn marion and less caron butler. it certainly gives them the flexibility to roll out some interesting line-ups. in a wide-open west they are in play for the conference title with this move. it also makes mo williams more movable if that helps them get another piece.
The trade assumes that Dallas would trade a playoff run this year for the chance to get howard / williams. that's a risk but one that i believe they would take given the chandler decision this summer.