Hello Everyone! I am a newly certified open-water diver who just returned from diving in ST. John. I was wondering why divers purchase BCD's that have such high lift capacities? From what I understand, the BCD's purpose is to fine tune bouyancy at depth and float you comfortably at the surface (not to say overcome the amount of weight your carrying). I guess what I'm asking is, once I'm properly weighted (regardless of exposure suit or equipment) wouldn't 5LBS. of lift make me positively bouyant? Thanks!