And 128k opus is perfect to my ears. I store all my music in the best possible quality FLAC files, but stream it to my phone in 128k opus. Such a great format, encodes very fast even with my Intel atom and sounds great.

I’m curious as someone with a local library, how do you stream it in a different format than it’s encoded in, from your phone?

Lossy to lossy transcodes always cause more degradation, so it's better to keep your lossy files in their original format without any re-encoding.

Easy transcodes to various lossy formats are the primary reason for a well maintained and curated library of proper FLACs (or ALACs).

The main advantage being that your can fit more great sounding music on your space-limited device. Disk space is cheap, but upgrades on your phone are probably not. Even if your Music collection fits easily, why not have more room for other media / apps?

I used to use Subsonic and one of the many clients. I don't know if Subsonic is still an option, but there are many server side applications, including a few forks, that fill that role. There are others that work with those same Subsonic clients.

It will allow you to choose a codec for streaming that is different than storage.

Plexamp does this automatically if requested.