Artist

WMP has two kind of artists in the navigation pane: the Artist and the Contributing Artist.
The Artist is called Album Artist in list view (column).

You have works performed by Gideon Kremer, by Martha Argerich and by the both of them.
In these cases you can use for an Artist:
Gideon Kremer
Martha Argerich
Kremer/Argerich

This makes it difficult to find all the works played by each of them.

The trick is to choose one you consider leading as the album artist and enter both their names separated by a ; in the Contributing Artist (Artist in the Advanced Editor is the Contributing Artist, they have some problems using consistent labeling).

If you browse by contributing artist, you have the all the works this artist is involved in.

This is great in case of Jazz to, the Album Artist is the band leader and as contributing artist you add all the cats playing on this session.

If you want to find the work where Coltrane is the band leader, you browse the Album Artist.

Sampler

It is also of use in case of samplers.
The Album Artist is labeled Various Artist (if you would use the name of the artist, you get as much albums as there are artist) but in the Contributing Artist you can see the performer.

No artist

If the Album Artist is empty WMP displays the value of the Contributing Artist (if available).
In case of samplers you can notice this as in album view the Album Artist is the Contributing Artist of the first track.

Use the Advanced Tag Editor to check this.