Allen is the greatest three-point shooter in NBA history, and he dares to take and make shots that have a huge impact. The Thunder will tell you how badly they were damaged in the NBA Finals by the three-point shooting of Shane Battier, Miami's top free-agent signing of last summer. Now the Heat can finish games with Allen scoring in transition and spacing the floor around LeBron James, Dwyane Wade and Chris Bosh.
The double-edged impact of this move is that it also damages the Celtics, who lost Game 7 of the conference finals at Miami and will go into next season as the Heat's top challenger in the East. The Celtics were hoping to bring back Allen and were offering twice as much as the Heat's $3 million annual exception in hope of keeping him. Had they succeeded, they would have entered the new season with a wealth of options on the wing between guards Allen, Rajon Rondo, Jason Terry and Avery Bradley to go with small forwards Paul Pierce and Jeff Green, who is expected to re-sign with Boston.
Now it's Boston that may be overwhelmed trying to match up with Miami's variety of options, especially now that James has developed his ability to score and pass out of the post. The Miami half-court offense that tended to stagnate in James's first year was moving more fluidly in the playoffs last spring as the ball zipped from shooter to shooter. Allen's tireless cuts without the ball and the defensive attention he commands far away from the basket will encourage more ball movement than ever.
When James, Wade and Bosh joined together in Miami, their goal was to recreate the championship dynamic of Boston's Big Three. Now they've succeeded in co-opting Allen, whose arrival by trade to Boston in 2007 convinced Garnett to accept a trade to the Celtics.
There is nothing hypocritical about Allen's decision to switch sides in the East's best rivalry. Allen has spent the last several midseason trading deadlines dealing with rumors that Boston would move him, and last March he was told that he had been sent to Memphis before the trade was rescinded. Among Boston's four All-Stars, Allen was the only one who didn't suggest personal animosity with the Heat. Pierce liked to goad them via Twitter, and Rondo and Garnett left the court without congratulating the Heat after Game 7. And yet no fans of the Celtics can complain that Allen didn't do everything he could to help them beat Miami over the last couple of years.
Allen struggled over the latter half of the season while dealing with bone spurs. But recent surgery should help him recover the form he showed in the opening months, when he and Rondo were Boston's best players. Though he'll be 37 next season, this move is likely to help keep him fresh. He is going to Miami to help win another championship, and he wouldn't have accepted the offer if he wasn't confident of fulfilling the promise.