pocket pairs as drawing hands

[EMcWilliams]

I know that it is very rare that there can be any generalizations in poker, and if this question seems too general and just plain ignorant, then I apologize. However, at what point in hands in NL Hold'em do pocket pairs no longer really become hands that you are drawing for a set and more are playing just the pair itself.

For example, when you play deuces, you are playing that as a drawing hand to a set, but aces your playing as a pair of aces.

I know there are examples where you have 99 and the flop is all low cards, so you are playing the overpair. My question is more towards pre-flop play in any position.