based on memory, so a little vague, but examples - access to various merchants in Bravely Default required you to have passed others. i remember this because i was sick with flu and spent a couple days with my 3ds and my daughter’s running/“passing” each other repeatedly so i could unlock everything.

to the best of my memory, some turn-based rpg’s (Persona? SMT? Etrian Odyssey?) would allow you to access customized personas/demons/teams? others had made available. like maybe someone had a really great high level persona (basically a pokemon) with a really great selection of skills on it and you could use it instead of trying to build the same thing yourself, before you might have normally had access to it.

so the latter type thing was cool and fun, but i didn’t get many of those. the first example is a situation where the game doesn’t really fully work without spotpass.