Your partner opens the bidding with one spade in 2nd seat. Right hand opponent interferes with a Michaels cue bid of two spades (showing at least 5-5 in hearts and an unknown minor). You hold:
You have a nice spade raise, but the overcall has robbed you of bidding space (a nice feature of Michaels). How are you going to cope? You could bid three spades or three diamonds.
Instead I suggest you cue bid three hearts (hearts is RHO’s known suit). By doing that, you convey to opener that you have trump support and at least the values for a limit raise.
Bottom line: Cue bid of an opponent’s overcalled suit promises an invitational raise or better in your partner’s opened suit (usually a major). Since it has become standard practice for most players, the cue bid is not alertable in this situation. Notice also that it reserves the direct raise to three of partner’s major to show eight to a bad 10 points — very helpful to partner in deciding whether to press on to game.