Filtered content, the ability to read posts from higher quality users with far less spam and noise, selection of languages, and more assurance that the relay will be maintained into the future since its operation is subsidized by the users. You can also get to know your relay operator, and you’re supporting the decentralized community infrastructure. Some relay operators will add new features that are requested by their users, so you can have a voice in how things are managed. You can also run your own relay, either as a personal backup, or open to other users if you have the interest and resources to do that.

https://nostr.how/en/relays