Tracks on an album can have tracks by different artists. For example, an album might be primarily by a single artist, but several tracks may have an additional artist or a different name. So, for example, 10 tracks have ARTIST set to Bob. But the 11th track has ARTIST set to Bob and Mary. And the 12th track has ARTIST set to Bob and Jane. If you set ALBUM ARTIST to a common value, say Bob or Bob and Others, then all the tracks will be seen as a single album. To be a single album all tracks should have the same value for ALBUM and ALBUM ARTIST.
ALBUM ARTIST (AUTO) is a special case where MC looks at the album name and if the ARTIST field is different for each of those tracks and ALBUM ARTIST is blank it puts in (Multiple Artists) for ALBUM ARTST (AUTO). Then the album is defined by the album name and the artist (Multiple Artists).
So, the approach that gives you the most control is to set ALBUM ARTIST to a common value for all tracks that you want to be a single album. That overrides MC setting Album Artist (Auto) for you and using that.
I just looked at one of my John Coltrane albums, which is a compilation of some of his best tracks from multiple albums. Some of the ARTIST fields are set to John Coltrane Quartet. But some are set to just John Coltrane. So, unless I specify ALBUM ARTIST, MC will set ALBUM ARTIST (Auto) to (Multiple Artists). Since I want the album to be displayed and sorted by just John Coltrane, not by (Multiple Artists) I just set ALBUM ARTIST to John Coltrane. However, when I list the tracks, I can display ARTIST and it will show me the original artist entries.
Hope that helps.