I did a fill-in with an old-style full big band (like in the '40s). Cool gig, but pages were always missing from the book, bass and guitar books. At the gig, the leader thought it would be nice to invite another bassist and guitarist to play as well, like that would make up for all those missing pages. Sheez, what a mess. I played one set and quit, telling the other bass player (a young cat) it was all his.
Another big band rehearsal had me and another bassist reading charts, except he was only following the changes and not reading the notes like I was. Another mess. I never went back.
That's my take on it. Two basses just don't work.
My wife and I both play bass in our band. We do this so that whoever is singing lead can sing "naked," and be more of a performer. We don't do that all the time; sometimes I'm playing acoustic, or keyboard, but no matter how we're configured, we always have only ONE electric guitar.
On the AC/DC song, "Whole Lotta Rosie" once you get past the last chorus, and the band is jamming, the rhythm guitar plays a huge part in the sound, and when I just played the bass line, and Arthur played the lead, it sounded too empty, so my wife jumped in, and played the rhythm part on her bass, while I held down the bottom on mine.
IT SOUNDS FANTASTIC! And it finally gave us a spot where we used both basses.
Next stop:
Covering "Big Bottom" by Spinal Tap.
It just seems like the best thing to do. We will leave out the keyboard part, and find a way to integrate some guitar.

