I think it depends on when folks were using Arch. I've been using it since 2007, and back then before the "conf.d" configuration file convention became common,

I think it depends on when folks were using Arch. I've been using it since 2007, and back then before the "conf.d" configuration file convention became common, it was very frequent that you would need to manually merge your local config files with the upstream one. If you screwed up or forgot, your system would be some variety of hosed. It's become much, much less common in the past ~10 years. I'd hazard a guess I only have to manually attend to an update once or twice a year now, where it used to be almost daily.