I find that knowing your NSS doesn't necessarily mean you will study harder, because you should've been working as hard as you can in the first place. However, I do like to know what mine is though, mainly to have a benchmark of my performance simply because it is comforting to know (particularly when your goal at selection requires a minimum score). At the very least it's a strong sense of curiosity and at the most it's that I don't feel comfortable just not knowing what it is (and there are quite a few others with that personality trait). I understand that knowing it is not the most important thing in the world, and that to know final NSS is impossible, but having some kind of concrete number at least takes some of the mystery away, which is what a lot of people want.