It is a good skill to have for example if you know you have 10 outs and there are 40 cards left in the deck 10/40 gives you a 25% chance of hitting your outs
Of course it is important to know the outs and calculate. For example, you have to know if a call is ok when you have a draw or if the price is too high. Or if you put your opponent on a draw and you want a call not to be profitable for him.
I just want to say that in some hands people just play with zero chance on the flop, call without having outs and win on the turn and river as a result...