I do split multiple artists in the Artist tag, but I wanted the same for Album Artist. I have an album, for example, by Elis Regina and Tom Jobim, who were separate artists and only released this album together. So when I group by artist in artwork (which uses Album Artist tag), there's an artist just for Elis Regina and Tom Jobim.. But I understand it might be difficult to do this.
And about multiple publishers, it's because I like to put both publisher and label in this tag, for example, Sony Music, Epic Records, 550 music; or avex trax (a label/publisher in Japan) and rhythm zone (a label within avex trax).