I've been using Apple TV since it first came out. Recently got the 4K version (3rd gen with 128 GB storage and wired Ethernet). We do have quite a bit of content (music, TV shows and movies). For music, all the original CDs I ripped to my Mac, then iTunes purchases over the years to include movies and TV shows.
Prior to having unlimited internet, for any TV shows or movies we tended to watch over and over, I would download them to my computer, then stream from that (i.e. incur the download just once).
Now, with unlimited internet, we just stream. I do have the Apple TV though connected directly to my Cable Modem via Ethernet. Even with a good mesh WiFi network and the home theatre being right next to the home office, the Apple TV 4K (and even Apple TV HD before it) started to drop connections almost once a day for a couple of months.