I am with the rest, adding voice to it allows you to give extra details as and when you need to and is way better than clogging up the screen with either annotations or having to open notepad to type instructions to the viewer. This allows them to see what youre doing throughout without distraction. Adding voice in my opinion will add quality to a screen recording and I doubt anyone will complain. The only circumstance I think it is better not is when your audience cant understand a word you are saying for example if they were all English and you could only speak a few words of English, in those circumstances it would be better off left out.