[rzzzt]

It was for me. I was using rsync with "--link-dest" earlier for this purpose, but that only works if the file is present in consecutive backups. I wanted to have the option of seeing a potentially different subset of files for each backup and saving disk space at the same time.

Restic and Borg can do this at the block level, which is more effective but requires the tool to be installed when I want to check out something.