[BluffTHIS!]

You want to play in a way that doesn't insure you lose the most when behind, and win the least when ahead. That is a dangerous flop in a raised pot, although hero does have the nut flush draw. So checking and calling a bet when made by someone other than a rock (adds possiblities of no straight out but someone just representing same), allows you to see what others do first. Of course against heavy action like a bet and raise then you fold.