Well, it isn't good against a slam. If your partner has an entry, you
will beat the slam whatever you lead and getting a ruff will only beat
it a second trick, which you usually won't need for a good score.
Meanwhile, you are giving up control of a suit where all the evidence
you can see points to it being a suit that the _opponents_ are going
to want to develop. It is very unlikely that your Ace will not take a
trick later, _vanishingly_ unlikely. You are much better off leading a
suit where you have some strength in order to develop (a) trick(s) for
your side.
It is good to lead a singleton Ace when it is a suit your partner has
bid or perhaps doubled to suggest a lead.
Otherwise:
If they are in a game-level suit contract and your hand's general
weakness suggests that your partner will get in to let you trump the
suit. If you probably have all of your side's high cards, the lead is
not tempting.
If they are stopped in a lower-level suit contract much the same
applies but your side's total strength is higher.
--
Will in New Haven