when to raise a draw on the turn?

[gopnik]

I've noticed that at higher limits players often raise their good draws on the turn (in position) instead of the flop. I understand why you would do it on the flop (value/equity, free card). But why would you do it on the turn? Only because of the folding equity? What are good conditions to make this move? I am used to playing micros where your folding equity is usually pretty small and you should bet/raise for value. Thoughts? Examples?