As Jan said, the unit will only introduce a certain amount of chlorine every 24 hours, and it's not enough to shock the pool.

However, you are correct in that putting more pucks in the canister will result in more chlorine being delivered to the pool at any given setting. I have 2 small pools with CL 220 feeders and if I put more than 2 pucks in them at a time, they will overchlorinate the pools in a couple of hours, even at the lowest setting.

I'd use the chlorinator to maintain ~ 1 ppm at the hottest part s of the day and with highest pool use and supplement with bleach when you need to shock or add extra chlorine. (you'll have to play around with # of pucks in the chlorinator and feed setting to find the 'sweet spot')