I find the better players resign earlier. They know when they are lost, and they know depending on your rating you wont blow it. Also the time controls.
Then it also depends on the amount of counterplay. Piece down in a symmetrical position, it's probably over. Piece down in a muddy position with lots of imbalances where there may be promotions it may be worth carrying on.
I'm playing a game now where I won their queen in the first 10 moves and they are playing on. It's 100% pointless, and we can't learn a thing.
But then I've also played games where I thought my opponent should have made me prove the win.
Around Chess.com there seems to be some question about whether it is better to resign when you know you are going to lose, or keep on playing. Personally, I prefer to play to the bitter, bloody end, and try not to resign. However, some people would call this dishonorable and unfair to the other player. My thoughts are that it really isn't dishonorable or unfair to the other player because in the end I'm just as dead, and he also has the satisfaction of a Checkmate (something I find far more satisfying then a resignation).
This is just my humble opinion. It would be interesting to see every one else's thoughts on the subject.