It may seem like a favor to Pierce, but I am not so sure he wouldn't rather collect his full salary this year with a team like the Cavs and then explore his options next year. He would be leaving a lot of money on the table just to join a team with a slim opportunity of winning it all.
Sure, if he gets bought out by the Celtics or a team wanting to shed salary, then it would make sense for him to join up with the Clips, but don't be so sure that it's a favor to Pierce.