@janettespeyer The main benefits we've seen are two-fold: self-reliance, and control.
Broadly speaking, relying on other people to administrate a server can be a bit of a compromise. You might have a great admin team, with dedicated moderators, tremendous uptime, and clear community policies. Or, you might not have any of those things.
The main critique of joining a community instance vs self-hosting can be summed up as the following question: how comfortable are you in having someone else make decisions on your behalf?