If you add a lot of new stuff to your library, you'll often need to add them to MusicBrainz yourself. I use beets and I currently have added 2697 releases (2543 release groups) to MusicBrainz.
I'm in the midst of a major music library overhaul and would not know how I'd ever get it done without Beets. For example, it's clearing out embedded images, fetching new hi-res artwork and verifying FLAC integrity, as I go through artist by artist.