If you are throwing away timeouts with 3 minutes left and not using your challenge given the number of incorrect calls during a game (many), I think it's fair to criticize the coach for not making optimal use of resources. But Mazzulla is hardly alone wrt poor use of challenges.
Further, it's probably possible to buy guys more rest with a strategically called timeout near the end of a quarter. Maybe even use the timeout to draw up a play. The Celtics have a better offensive rating after a timeout than they do in the half court overall.
Edit: To be clear, this is nitpicking. I don't really care whether Mazzulla does/doesn't call timeouts. I do care about how Celtics coaches throw away points nearly every game because they don't challenge effectively, but that criticism applies to nearly every NBA coach.
Further, it's probably possible to buy guys more rest with a strategically called timeout near the end of a quarter. Maybe even use the timeout to draw up a play. The Celtics have a better offensive rating after a timeout than they do in the half court overall.
Edit: To be clear, this is nitpicking. I don't really care whether Mazzulla does/doesn't call timeouts. I do care about how Celtics coaches throw away points nearly every game because they don't challenge effectively, but that criticism applies to nearly every NBA coach.