I didn't used to think this was so obvious, but I'm so annoyed with the absolute frequency of ads on chromecast that I'm about to try and force my chromecast to look at some local jellyfin server or whatever and just pre-download every video I want to watch.
That being said, up until literally a week or two ago, I had a data cap of 1.3TB/mo. It'd take me a while to hoard much data after all of my normal data usage. If you stream a lot of video, 1.3TB is shockingly little.