In poker we only get to play one hand at a time. As a result, we typically find ourselves asking "How should I play this hand, on this street?"
When we do so we're going to encounter some spots where we simply have no idea what to do — because we don't understand our own range of possible hands.
I played a hand in the World Poker Tour National Killarney event last weekend that shows how thinking about your whole range of hands can guide decisions throughout postflop with any particular hand.