The Zone System is most effective with sheet film, but that doesn't mean you can't apply it, at least partially, to roll film. I usually try to keep track of my exposures, and then develop for either the majority, or the most important exposures on each roll. Sometimes, I'll load two roll film backs for my RB67 with the same film, and use one for high contrast scenes, and the other for low contrast.

Edit: As usual, I've been beaten to the point.