I knew about Wi-Fi and cell towers being used to improve location data, but this is nifty too:
Ultra can cache orbit predictions for up to a week. That means you can go offline and still get an immediate location fix because you don't need to wait for your watch to decode that information; it's already there.
I used to carry an independent GPS device while hiking, but mostly stopped because my phone gives much better data with fewer anomalies. I still sometimes carry it on trips so I can match the GPX data to photos with Houdah Geo.
On that note: I kinda wish I could export GPX recordings from Health/Fitness. It feels redundant that I have a "hiking" workout and a Gaia recording running at the same time. Gaia's able to export tracks as a workout, but of course there's no heart rate data etc. in Fitness if I do it that way.