They're both role-players. From that type of player, defense and rebounding is a lot more important than offense. Offense starts offering diminishing returns. There's a limited number of possessions to use but in every defensive possession you need 5 guys to defend.
Offense is supposed to be played with all 5 guys on each possession too if you are sharing the ball and not playing iso. There is no diminishing returns. Also offense and defense couldn't be separated, they affect one another. For example if you turn over the ball less you give less chance to opposite team for high% transition offense and this increase overall quality of your team defense.
In Clippers game Krstic & Garnet have been the only healthy bigs on a team and couldn't allow to be fouled out with no backup. And Clippers had enough of big bodies (Jordan, Caman, Griffin) to play with more energy and to rotate them better to be more fresh.
Also, from the trade the only game when Boston was inferior in rebounds was against GSW (and all difference was in offensive rebounds).
Up to this point Krstic extremely overachieved in Boston's uniform. And he is still learning rotations and plays. We need to wait minimum few more weeks before any conclusion how this trade affect Boston.