[pzhon]

You need to consider several additional factors:

[img]/images/graemlins/diamond.gif[/img] How often will you win if you miss the flush?
Most of the time, you have other ways to win. An overcard might provide 3 outs. Against someone with ace high, you might have 6 extra pairing outs. You can get a runner-runner straight or trips. Your opponent's low pair might be counterfeited, e.g., your opponent has 33 on a board of 78872. You might be ahead of someone with no pair. These possibilities add up. A flush draw with no obvious other draws often wins about 38% of the time against a high pair.

[img]/images/graemlins/diamond.gif[/img] How often will you make the flush and still lose?
Someone could have the nut flush draw. Someone could have just one high card of that suit, and the turn and river could put a 4-flush on the board. The board might pair, and your flush could lose to a full house. Flush draws typically win only about 25% of the time against someone with trips or a set.

If the flop is monotone, you can't treat a low card of that suit as a flush draw against multiple opponents.

[img]/images/graemlins/diamond.gif[/img] How much will you put in on the turn if you miss?
This is a serious consideration both in limit and NL. If you raise on the flop, you may get a free card in limit, and you may win the pot in NL. The free card is not free, but it is better than half-price because if you are behind with a flush draw on the flop, you are often only a slight underdog, so you don't mind seeing a lot of money go in on the flop.

In NL, if your opponents routinely bet a lot on the turn after you call on the flop, then fail to pay off if a flush card comes on the river, they succeed in making flush draws unprofitable. However, they will pay too much when you have a straight draw or slow-play strong made hand, and you can play weak draws with the added value of being able to bluff on a flush card.

[img]/images/graemlins/diamond.gif[/img] How much extra will you win after you make your flush?
If you have position on your opponent, it is much easier to charge your opponent after you make your flush, particularly if you make your flush on the turn.

In conclusion, some flush draws are stronger than others. If your flush draw is too weak (you are out of position, you may be drawing dead, it will be hard to win other than by hitting the flush, you are drawing to a low flush), you won't have the odds to play it in a large multi-way pot. A strong flush draw (you are in position, you have the nut flush draw, many other potential outs, your hand might be good already) can be played heads-up even when the pot is small.