I have seen some advanced TC systems featuring advanced launch control features which help to limit wheelspin in drag-style starts. If the vehicle has so much grip that it is not traction limited at the start, (what a nice problem that would be!) then TC will not help.
Most production-car TC systems will slow dowan a very good driver on a road course when engaged. As time passes, and the "competition" mode of such systems becomes more advanced, that may be less and less of the case. In the meantime, advanced/aftermarket race-bred TC systems are definitely of a help to a road race car (when they are reliable
) - witness the recent banning of TC in F1 in an attempt to slow the cars down.