depending on potency, method of smoking, etc.
Heavy use: Smoking on a consistent basis, wake and bake, and every hour or so. If you are smoking more than 2 grams a day of B-A grade cannabis, you are not only wasting your money/time and effort, but you are abusing cannabis. You will start to see negative side effects if you smoke this much.
It doesn't matter to me how much you are smoking as everyone has a differing tolerance level, but moreover, how often you are smoking. It doesn't matter if it "gets in the way" of things - that's call priorities... we're talking heavy use/ abuse here. To clarify: if you are smoking daily, several times each day, this is heavy use, overkill, and clear abuse. Generally this will eventually equate to 3 grams of headies a day (to yourself, not shared, so do the math yourself).
It's not hard to tell when you are using something as a crutch - this is what I would consider abuse or heavy use. Daily smoking =/= heavy use IMO.