When the system evolves, you need to change things. State structure also evolves and you will refactor and rework it. You'll rename things, move fields around.

URL is considered a permanent string. You can break it, but that's a bad thing.

So keeping state in the URL will constrain you from evolving your system. That's bad thing.

I think, that it's more appropriate to treat URL like a protocol. You can encode some state parameters to it and you can decode URL into a state on page load. You probably could even version it, if necessary.

For very simple pages, storing entire state in the URL might work.

I think it depends on the permanence of the thing you’re keeping state for. For example for a blog post, you might want to keep it around for a long time.

But sometimes it’s less obvious how to keep state encoded in a URL or otherwise (i.e for the convenience of your users do you want refreshing a feed to return the user to a marker point in the feed that they were viewing? Or do you want to return to the latest point in the feed since users expect a refresh action to give them a fresh feed?).

You can always do versioning.