If you're a sports fan you've probably heard the phrase "addition by subtraction."
It's a nice way to imply that a player's departure is actually beneficial to the team he leaves.
Sports aren't always so easy to predict though.
Is Allen a future Hall of Fame basketball player? Yes.
Is Allen one of the best, perhaps the best, three-point shooters in NBA history? Yes.
Will the 2012-13 Boston Celtics be a better team in his absence? Yes.
If you're a Celtics fan, you probably loved Allen. You may even still think the world of him. That's fine. He's a great basketball player.
He had run his course in Boston, though.
The most telling thing about Allen's departure was that he took less money from the Miami Heat than what the Boston Celtics were offering.
That was his right as an adult, and as a basketball player. He was no more committed to Boston than Boston was to him. After all, the Celtics nearly traded Allen last March as the NBA's trade deadline approached.
So Allen had a right to want to leave, and he did, and that's fine.
The Boston Celtics' current run of success has been centered around defense. Allen, even in his younger days, was never known as a great defensive player. When Allen was hobbled by injuries last spring, second year shooting guard Avery Bradley took over as the starting shooting guard.
While Bradley is not nearly the outside shooter that Ray Allen is, he's a far superior defensive guard.
Additionally, Allen is no longer a player who can create his own shot. In order to free up Allen for his deadly accurate three-point shots, the Celtics would need to run their entire offense around him. Multiple screens would need to be set, and while the results could be a made three-point shot, the effort and commitment to creating that opportunity was limiting the rest of the offense.
Allen's other statistical production has waned in recent years. He's averaged 4.2 rebounds and 3.5 assists per game over his 16 year NBA career. In 2011-12 he only grabbed 3.3 rebounds and 2.5 assists per game.
Those aren't massive drop-offs, but look at what Allen's departure spurned.
Not only will Bradley, a superior defensive guard, be starting in his place. The Celtics also brought Jason Terry and Courtney Lee on board.
So look at the Celtics now, and then look at the Celtics with Allen.
If Allen had stayed, there would have been tension regarding Bradley, and his role as the starting shooting guard.
Instead, Allen is gone and Bradley now has two more complementary teammates to play with in the backcourt.
Lee adds size and athleticism that the aging Allen could not provide. Terry, who finished second in the NBA in made three-point shots in 2011-12, will be able to make up for the lost long-range accuracy.
Terry is also a better transition player than Allen.
The Celtics are deeper, younger and more versatile without Allen.
Finally, there's the issue of actually wanting to be on the team.
Ray Allen didn't want to play for the Celtics in 2012-13. There's nothing wrong with that, especially since the Celtics are probably better off without him.