It's a good idea to take a break from pot every once and a while, just to guage what affects it is having on your life, body, mind, etc. The same goes for alcohol (and probably junk food, too). Every year, my spouse and I take a month off from the herb. That way we know if we're suffering any ill effects (so far, we aren't), and we feel better knowing that it isn't a big deal to stop.
Of course it's different for medical users that may depend on pot to eat. My spouse was just diagnosed with Crohn's, so she may be abstaining from her abstinance for a while.