It's funny that you mention CVS. I went to use the human checkout at CVS last time I was there because the line for self-checkout was so long, only to be told "in order to check out at this register, you need to have a CVS extra-care card".
You really have to be able to judge to self checkout ability of the people in line. Some will get stuck for 5 min before a clerk comes to do it for them.
I can be through the whole process at CVS (with some random item like a birthday card) in about 30 seconds.