
If you run a public server with special features such as extended post lengths, additional poll options, rich text etc, you might want to mention these in your server's description.
A lot of new people join big stock Mastodon servers and aren't sure about the differences between servers. Something very concrete like longer posts is a really good way of getting them thinking about moving.
It's not the only reason to move, but it's a good way to get their attention!