Storage is cheap. Plus you might want/need to re-encode to another format down the line and any lossless format is better as the master copy.

One day you might want to transcode - compression artifacts may well not be audible in normal use, different compression algorithms drop different bits though and so the result of transcoding between compressed formats is quite often an audible (even to my distinctly non-golden ears) loss of quality. Thus FLAC (as a reliable lossless format) - or even WAV (I chose to take the 2:1, 3:1 compression of FLAC over WAV personally).

While true... I figured out how little I was saving by not doing FLAC. And there wasn't a point in saving that storage. I've got plenty, and that's with 5 bays still empty in the Synology.

I only wish I could do the same with video.

I’ve gone back and forth on the question but with storage costs as they are I always have a Source of Truth in FLAC.

For listening I figure I’ve spent so much $$ on my setup I’d be dumb not to ensure the source is not perfect too - for free.

10x? More like 2-3x

Besides the fact that storage is cheap, FLAC has a more ample metadata model than MP3 and I'm already used to working with the toolchain for that metadata.