If you mean an orbital polisher, one of the £20 jobs, they're as good as useless in my opinion. An angle grinder type one is the kiddy. I'm no professional, but I would only use G3 for compounding new 2 pack paint, G10 for reviving old paint, used with a trigger spray of water to keep the job wet. Keep a hose nearby to hose off after each panel, it's a bitch to remove once dry, especially on black trim.. As has already been said, be careful of corners and swage lines, it's easy to hit primer here. And, once it's mopped, keep it nice with regular waxing, I used to use autoglym ultra deep shine, but i've recently started using stuff called greased lightening showroom shine, which is a waterless cleaner based on carnauba wax i believe. It makes polishing 10 times easier.