It doesn’t store media forever that is routinely cleaned and configurable in the administration settings for the instance. The content cache, which is database storage used for the text and meta-data of posts is more typically an issue over time because this requires commands to be run on the server to free up space, which many people do not do. https://fedihost.co/blog/slug/managing-mastodon-storage

Perhaps you could write up the sort of guide you are talking about so I can see what you mean? I haven’t found people respond well to hitting them with much more than this upfront, and they get anxious when you don’t give them some specific recommendations to get started.

I wonder if I should make a fediverse animated gif or short mp4 that can be dropped in whenever needed.