drawing with threeflush on board

Let's say you have AJo (jack of spades) in a typical L/P game. three opponents or so limp, flop comes spade spade spade. when is it worth drawing to the third nut? i usually almost lay it down right away, but i don't know if it's correct due to pot odds blah blah.

[toss]

Depends on a lot of things. (Reads, # of players, position, table image, etc.)