Going to close our 27' above ground pool this weekend and was reading the winterizing instructions. I noticed that they suggest shocking before draining the pool rather than after draining as I've been doing the past few years. Seems kinda wasteful (and bad for the environment) to add so much chlorine which you're going to dump in a few hours. Just wanted to know if there's a good reason for shocking before or if I'd be ok to continue shocking after I've drained?