Pretty much never use rare candies. 2 reasons:
1. Paranoid logic. The higher level your mons, the more experience they give... so technically the most efficient use of them would be at 99.
2. Old habit: as a kid, before I looked up stuff online, I would save all my candies to check what moves a mon would learn through level up (then reset the game).
After I discovered iv calculators, I'd use the same technique when breeding to get more accurate iv estimates.
