People like to make loose calls of over-bets on two-tone boards.

Against terrible players it's bad because they're not likely to blow you off the pot on the turn and they will pay off when you hit.

Against tight players, their bet/raise ranges can be tight enought that your'e running into a hand too often (see first point.) Also, many of these guys will price you in.

I mostly like playing draws really fast against guys who are capable of betting/raising light and folding to aggression. Most people like that are playing at least 200NL.