Mostly things like recovery time recommendations, body battery, training status, some scores, stuff like that.
There are tons of secondary apps that provide all of those things. Fundamentally the Garmin records less baseline parameters than the Apple Watch does for instance it does not do blood oxygen level monitoring, so whatever stats it’s providing are just software algorithms.
honestly, if you're asking that question you don't need a garmin/coros. I'm a long distance trail runner, so I appreciate things like a cleaner heart rate (strap), hill climb alerts (length + degree), food alerts, loading a map (mandatory for races to have the route as GPX on my watch). Also stuff like training readiness, recovery etc. Stuff like that. If you're a recreational jogger, you don't need a specialized watch imho.