I'd also strongly endorse its on-the-street mobile app counterpart, StreetComplete. Splitting stuff into tiny tasks you can focus on really helps if you're just out on foot in an area.
Similarly, `Go Map!!` is an iOS app that makes editing OSM data easy.
Adding missing features is one of my favorite things to do while traveling, and feels like a way of giving back (“take only photos, leave only GIS traces”?)
I've occasionally used the CoMaps OSM editing capability to just get the basics in before doing the big work in JOSM, or more likely the web editor. Now I'll be looking into MapComplete much further.
Could be but needs a serious UI/UX revamp (easy). Maximally remove friction when asking for user contributions. Like literally on the first page it puts adding public clocks, I repeat, PUBLIC CLOCKS (and other such things), on equal footing as adding a restaurant. Like, no.