I recently started using a 1TB Seagate Expansion USB3 disk connected to my Roon Core running on a i5 NUC (Debian Linux). The main reason for this was that my NAS (older Netgear Pro 2) did not supply a full set of file info over an SMB mount, resulting in real time folder watching not working in Roon (like @Ludwig above) .
The unexpected then happened; sound improved markedly with the music disk directly attached. Better bass and more detail overall, but still a more relaxed sound. I’ve checked back and forth a couple of times and the change is unmistakable. I use rsync to mirror the music folder on the single disk back to the NAS where I already had a backup regime.
I have a small library. Only 560 albums with around 7000 tracks, mostly FLAC rips from CD, but also downloads in high resolution.