Do I cap this suited ace preflop?

[detruncate]

It has to do with who has limped and what their likely range is. You know that nobody has liked their hand enough to raise. Your 8 kicker will often give you the best ace. You'll flop a flush draw about 1 time in 8.5. The hand is further strengthened by the times you flop two pair+ or some sort of straight draw. You'll often have at least a backdoor draw to help rescue you when you're dominated. You have position + iniative to help you maximize your profit post flop.

When you don't think your hand has a clear equity edge but you probably have enough implied odds to play it you obviously want to get in as cheaply as possible. When you don't know anything about the strength of your opponents' hands (because you're in early position) you're usually better off limping unless the table is such that you should be folding these sorts of hands or raising more than usual from ep.