Upload & Sell: On
It really depends how much you want to match your ambient. Some people like having the background go super orange and don't gel at all. I slap a full CTS on in most reception situations and the background is still a bit warm, probably 2500k in most situations, while I'm shooting at 3200k. Then there's people that like in between and shoot with 1/2 CTS.
How much correction is a different discussion. Many people, myself included, think Canon over-saturates reds for skin tones, and many people then find CTS to be better than CTO.