If this option is enabled then matching will only occur if every song on the album was matched by a file in our music collection. This means that we ensure are matches are to an album with same number of tracks, but it will prevent us matching any incomplete albums that we have.
If we have only this option enabled it means that any album that is matched must be completely matched but this doesn’t have to be on a folder by folder basis, so for example if we have a folder containing 10 songs that failed to match any album but existing metadata in the songs creates two groupings of 5 each, then one of those grouping could be matched to a 5 track release that would be okay.