They don’t top off. It’s a misnomer really. What you’re actually saying is you download your mags by one. Nothing wrong with that if that’s your thing, but effectively you have made your 15 rd. Mags 14 rds, your 8 rd mags 7 rds, etc.
I’m not concerned with what other people do nor do I pass judgement, but all the posts attempting to give some tactical reasoning behind downloading a magazine by one are bunk. Or at least they don’t pertain to me. My guns get shot a lot. I train a lot. Never lost time or had a failure due to carrying a fully loaded mag.