I have noticed that if you don't resign in a lost position and go through the game that is essentially torture from that point on, you just ruin your session. You play the games to follow in a foul mood and lose more games.
Its best to acknowledge a game losing mistake and resign.
It's important to remember that you often learn more from the games you lose than the ones you win. I resigned in a drawn position in a club tournament last week; if I had just played on I'd probably earned have half a point instead of 0