This is one of the topics that always creates a lot of differing opinions. Personally, I am of the "smoke one bowl in a pipe, let it rest for several days" school. (Sometimes I will smoke two bowls in the same pipe in the same day, but not often.) Other puffers will smoke multiple bowls in one day, then let it rest for a number of days.
How long is "a number of days"? This seems to be up for debate, too, but the consensus seems to be that you rest a pipe a number of days equal to the number of bowls smoked. My rotation is large enough that it's about a week between bowls.
At this point in a forum discussion, somebody will usually chime in with a comment about his granddad, who had one pipe, and all he smoked was Granger, and when the pipe went sour he threw it out. Yeah, the old timers used to do it, but that doesn't make it best practice. :puffpipe: