My experience a few years ago just giving Briar a try for fun was that both parties had to be online at the same time to relay messages (since there's no normal servers) and that it drained my phone battery quickly when I was online. Not practical.

I was thinking it would be nice to be able to run some sort of node under my own control that could buffer those messages. I feel like there was even an option to do that for phones, where someone could help relay messages between two friends, but I could be remembering wrong. At any rate, it would be cool if the desktop app could play this role.