.uuid files are how PhotoStructure ensures a given volume is referenced consistently even when drives are relabeled, or mounted on different paths, or accessed from different computers.
You can disable
.uuid writing by setting
PS_WRITE_VOLUME_UUID_FILES=0 (or changing the
writeVolumeUuidFiles system setting to false.
If you’re not expecting to open your library on another device, and you don’t have mountpoints that change names (like external drives), you can just disable this feature and be done with it.
More details are here: