I am a big fan Ray Allen as a player and an individual.  I wish him the best in Miami.  I only wish he was going to another team.  But, Miami may best fit his style of play.  One reason is that Lebron has finally realized that he can't do it all and learned to pass off when getting double teamed. This alone will allow Ray to get a lot of open shots. 

On the other hand, Ray's departure gives Doc more options as to who to play during any part of a game.  Over the past 5 years Doc relied heavily on the same line-up schemes.  It worked out well, but I doubt the team reached its true potential because of it.

This year, after Ray got injured, Doc was forced to trust his bench.  He couldn’t rely on his standard 'formula coaching' because Ray was unavailable. His typical Modus Operandi had been for the starters to finish the game regardless of how well the bench had been playing.  Ray's injury allowed starters and bench players to work together.  For the first time Doc showed confidence in Bradley, Dooling, Daniels, Sasha and Pietrus.  He didn't treat them like rookies when the game was on the line. He wasn't afraid to play them. (Sometimes I feel that Doc forgets that his bench players used to be starters and can handle just about any situation.)

Before Bradley got hurt Doc mixed and matched line-ups in a synergistic way.  I think it was the best coaching Doc has ever done while he’s been in the NBA.  Hopefully, he will continue to do this.  I’m not trying to discount Ray’s role in winning over the years.  I just feel Doc didn’t maximize his bench’s potential because of his loyalty to the ‘Big Three’.
 
On another note, I have a feeling Ray may eventually come to the conclusion that he made a colossal  mistake leaving Boston.  Sure, he doesn’t have to deal with Danny or Rajon any more, but he did give up his biggest fan,  Doc Rivers.  Doc was loyal to Ray to a fault.  He played him regardless of how poorly he had been playing or how much pain he felt.   Chances are he won't have that luxury in Miami.  It’s possible that if he's injured and/or not playing up to par...he'll be sitting. That never happened in Boston.  Ray may win another Championship in Miami, but if he's not 100%, there is a good chance he'll be doing it on the bench.