Tethering when working out and about is a big factor but even things like automatically backing up photos and videos after I capture them takes a lot. I also go to a lot of areas where internet speeds are terrible but 4G is faster so I use it over the wifi there.
I basically use it all the time when out and I am lucky enough to be in an area with really decent 4G speeds.
I knew when I switched to fully unlimited from my old contract I would use a lot but I too was surprised it was that much, its really nice to be able to just use your phone all the time wherever without worrying about data although I still need to carry a battery pack 
If I forget to download something to watch on a flight I can just grab it and its almost always faster than the airports lounge wifi as well, it just so nice to not worry about data and go nuts doing everything a phone can do but people dont use it for because of data fear.
My data (iOS) use since I reset on Jan 21th 2019 when I got my new contract.