Thank you for answers! Well my iMac is a little beast, so there’s no problem with work on original files – I just think to make optimized media from it, because how Larry Jordan says “For all editing where you are adding effects, color grading, or just want the best performance, optimize all camera native media.”
As I read about it on multiple sites, everyone agrees that convert files to optimized is good for quality in post process, which I’m going to do in my movies. BUT I’m still learning, so I’m open to all advices from You 🙂