[4_2_it]

You bet a draw in NL for several reasons:

1) To take down the pot immediately. (My highest success rate is on non-Broadway boards.)
2) For deception. If everyone checks and the draw hits and you 'wake up', you probably aren't getting paid. Betting with a draw can allow you to make a nice 2/3 pot bet when the draw hits. Now your opponent has no idea whether you are milking him, bluffing or just trying to get a TP-like hand to showdown.
3) Win a big pot when the draw hits.