Maybe not a wide use case, but the first thing that comes to mind is for people who work outside an office (law enforcement, for example) to collect data on their device as they do their job, then have a way to upload it into a web app when they return to the office, and not be sending it over a more public network while in the field.

Pairing your phone with your pc for realtime inputs w/o going through internet.

For example https://www.airconsole.com/ turns your phone into a gamepad for multiplayer browser games. But I think they are using web sockets or webrtc right now which is kind of silly when everyone is in the same room looking at the same browser.

Not a use case per se but, I think it could be useful in combination with Progressive Web Apps (which can work without an internet connection) to control bluetooth devices without installing an App.

It might be nice if My PC knows my phone is there a notification doesn't need to buzz my phone too.

The physical web - you can now interact with physical devices using your phone (or laptop I guess?) via BLE. Importantly, the devices don't need network connections (which is a pain).

Configuring a Fitbit directly from their website?

It can be used to access a company's own hardware.

You can browse Hacker News with it.