Protecting Draws and Buying Outs

[waynethetrain]

On page 158 of SSH it discusses protecting draws and buying outs.

I want to make sure on understand this section correctly.

The reason we should be willing to raise with our nut flush draw in the example even though we would be facing several players with 2 bets (and thus increase the chances they would fold and we would lose customers) is because we have 2 overcards that we would like to protect in the event we catch one on the turn or river in this big multi-way pot. Also, the raise has decent value because 2 players are already in.

Suppose however there was only 1 player in prior to our turn to bet (the bet came from our immediate right). Now the raise would not be good value on the flush draw if we knocked out all the other players as a result. However, it would still buy some outs.

So what is the right move in that case?

Suppose we have a 4 flush without overcards. Then wouldn't we be better off not raising unless there were a few callers already in because we don't want to KO customers.