There is value to running your own relay such as having it as an archive of your posts and other stuff, and also to serve as a caching proxy to reduce client load, and a private server for stuff you don't want to spread around, like drafts. Also with nip 29 it can be a more private way to run groups. Additionally a relay that is combined with hornet/blossom can serve as a replicated and encrypted data backup. I think the use cases will continue to grow.