between your device

Thats the part right there. Its for not your device to access.

Like a self- hosted website/blog for example. Or taking the complexity of “start this before you try to connect to my eBook server” for your BIL, or “OK mom, when you want to watch the home videos I converted to digital you have to do it only from your phone, press this first, then share to your TV”.

That is the part I think you are missing. Use other than yourself and your own managed devices.