A lazy cat in human skin, an eldritch being borne of the '90s.
Most websites track IP addresses, keep them in a database, and use them for various things. You can find a lot of information on this online, however in the case of non-profit social media like Mastodon, it can be useful for tracking bad actors and blocking them from access. Most of the time they are used for commercial purposes.
I concur, that’s one for the back pocket!