Here's how I look at it. When I play craps I risk my initial buyin. Usually I'll play to one of two conditions.

1 - I hit zero. I'm done.
2 - I get to about 175-200% of my buyin. Now I start taking money off the table from each win (a bit like rob's soft profits). Maybe I put a chip per point and odds pay in my pocket. Now I decide that I'm done when my chips on the table fall back to 150% of my buyin. And I count the extra chips in my pocket at the cashier.

Under this system if I get to 200% and for some reason keep playing and hit a cold streak, I'd consider that I lost at least 150% of my buyin since that was my exit point and I ignored it.

I don't consider my active bets on the table as really mine, even though in theory I could take many of them down and go home with the cash. I only consider chips in my rack as mine and some of the I consider in play since you have to risk some to play.

In the end, I always consider that if I lose my buyin, did I get the entertainment I was buying?

Sometimes I have a really long session that doesn't go up or down. On these I'll leave when I'm tired or the wife has had enough of my game.