I never do it. I should, because I'm (if I may be immodest for a moment) a really good writer. I've had over 30 plays produced in the past 20 years, but I'm also (if I may be self-effacing) a TERRIBLE actor. If I'm not just saying what's coming to mind right in the moment, then I sound more wooden than a plywood box holding cedar planks. So I let my editing program do all the "scripting" for me. Usually, I can improvise a really decent sounding video, if I slow down and just go from point to point.