thermal throttling...bad?

[chinkee]

i think i read something about disabling thermal throttling when oc'ing the 6800, but i was just curious why. what does thermal throttling do? mine is set to 50% by default. i have successfully unlocked 16 pipes and 6 vertex, but if i try to even oc my memory or core, rivatuner says that i don't pass the test. do i have to disable the thermal throttling to OC? i even got the silencer rev 5 for my card..