The left most lane is for passing, not driving. Once you are done passing the cars on your right, you are supposed to come back to adjacent lane on the right at next safe opportunity. If you keep driving for too long in the left lane you 'can be' ticketed for 'obstruction of traffic' (if driving @ or < 100 KMPH) or 'speeding' (if driving way over 100 KMPH for an extended distance).

This is what I was instructed while learning to drive - ultimately it is the officer's discretion to ticket based on 'circumstances' at the time of event.

My 2 cents.
Hiren