> So it's either a linux learning toy, or an integrated component within another product, and not much in between.

Raspberry Pi are excellent at being general-purpose, full-Linux boxes that consume very low power (some can idle at <1W). Perfect for ambient computing, cron-jobs, MQTT-related hackery, VPN gateways, ad-blocking DNS servers, or anything else that isn't CPU-bound, but benefits from being always available[1].

1. In my case, this ironically includes orchestrating higher-wattage computers via Wake-on-Lan and powering them down when not needed