The key thing is that all messages are signed and have a few standard fields, making them easy to replicate across many relays while maintaining the ability to verify their origin. And the second thing being that it is based on websockets, allowing the client to maintain an open connection and have new data be pushed instantly rather than relying on polling.
Yes as with many things these days it just makes it easier to integrate with existing systems, like web browsers. So you can have an entire client built into a web page without needing special server software to translate between NOSTRs native connection to a websocket. Plus it makes hosting easier in some cases.
