Hi,
In my experience it depends on the players your against but the pot odds for a flush draw at the flop are surely enhanced by the fact that if you raise or bet at the flop you may close out the hand right then on the semi bluff adding significantly to the win column in the overall return on your bet investment. Also you can then check if your flush comes disguising the hand and possibly enticing a bet on the river from the oponent who may even call a subsequent raise.
This vastly increases the profit from flush hands that are otherwise often damp squibs. When playing against better players you just are not going to make much unless you disguise your hands. Also if you do lose the pot it makes you look like a looser player and that can improve action on more conventional pairs and other made hands on the flop. If you "feel" your playing against better players it is hard not to tighten up too mych and then you are a sitting duck especially to big stacks. This method has certianly transformed my profits recently. (like I actually have profits now!)

Just my hapence worth.

Scott