On android, when you click a link that has an association with an app you get the choice to open the app instead of being redirected to the website. Right now every app developer for the fediverse needs to maintain a list of instances for this. If you had a protocol instead you would only need to specify the one.

Apps (at least on android, no idea both iOS) could claim support for the protocol. Removing the need to claim hundreds or thousands of addresses.

I was a bit cautious because of the "source-available" code. But it's just a standard CC-BY-NC-SA. So no problems there.