From the perspective of user control, having a Nostr public key and publishing notes on several relays is akin to owning several personal websites. The relays function more like cloud servers. 

This is entirely different from registering an account on a social media platform. 

The Nostr public key is the core entity, while the relays are the medium. nostr:note1xyrgrk3tekwax873xvepjjdm4jlhy7v4k6rkzmv7pfsmwkusj6ps3qurqm