What does `--consider-other-fs` option do?

What does --consider-other-fs do in restore-start? What does it ‘consider’?

During restore it deletes files that are not in the backup (e.g. created after backup took place). If you specify --consider-other-fs it’ll descend into other file systems below the path to be restored and delete files/directories there as well, otherwise it’ll skip other file systems.