You can run a clean fast line that minimises trail erosion... locking up your brakes and skidding through shows intent for disregard to preserving the trail. IMHO, if I've overcooked my entry speed into a turn and it's a choice between slowing down or skidding through then I'll slow down. I most likely want to be able to ride that trail again in the future. If you made a mistake in neglecting to keep your speeds appropriate for the conditions of that portion of the trail then suck it up and slow down. Doing otherwise shows a sense of inconsideration on your part.