One of the interesting aspects of Hanabi is that there really isn't enough turns to fully hint. So with every hint, you must ask yourself not just "Why is s/he telling me this?", but "Why are they telling me this now?" At least in the group I play with, the hint is presumed to be immediately useful, but you may have to make some deductions and take some risk to make a play.
Hints made to other players can matter, too. Suppose you play after me, and I make a hint that you can see would make the next player play an unplayable card. You know that I wouldn't make that hint unless you had some course of action that would fix the situation. Since spending a hint to make you fix things via a hint is silly, that leaves playing the card you'd otherwise discard. So you can interpret a hint for an unplayable card you can see as a hint to play the oldest card in your hand.
And it can go a level deeper, where the card you played blind is a 5 (or some other card incompatible with actually making the hinted card playable). Since they see that you thought the card wasn't playable, and then it didn't become possibly playable after your play, they now know that the card isn't playable and can be safely discarded. This isn't actually much better than just direct hinting, though, so the straightforward play is higher value. Both have advantages over straight hinting, though.
