Honestly, the way the Celtics were shooting in the 4th quarter last night, we needed someone with the confidence to step into shots. The series could very well be tied by now if the Celtics didn't turn into a bunch of bricklayers when they had some wide open looks. Inexperience and nerves caught up with some of the players yesterday, and having a heat-check guy like Thomas take some iffy shots is better, and arguably higher-percentage, than watching hot potato.
On the other hand, that's what Thomas is. If he doesn't take those maybe-good-but-maybe-bad-especially-if-he-misses shots, he becomes a borderline liability, kind of like how Rondo is a liability without the ball in his hands (although Thomas' deficiencies, namely height, are somewhat made up for by his shooting ability.) I see Thomas as a shorter, slightly-better decision-making version of Jason Terry that can drive to the rim more effectively- a borderline starter, but someone you'd prefer to have off the bench as a combustable game-manager. Basically, a step up from Patty Mills but below a Tony Parker.