Well, I can think of a couple of reasons to haul one of those monsters around. 1) If it’s an 11-string (or 8-string, or doubleneck, etc.) it’s probably a handmade, boutique bass that has a lot of thought put into the finish, shape, and wood. In other words, it’s pretty. And expensive. 2) You want to show off your mad bass-playing skillz by showcasing that you’re a) badass enough to know what to do with 11 strings, and b) (referring back to 1 above) serious enough about it to spend the cheese on an expensive, custom bass.
In other words, I think it’s all about style over substance, and seriously, if 4 strings was enough for Bootsy Collins, it ought to be enough for your lite fusion studio project. Hell, lord knows I’m no fan of Jaco Pastorius, but he had massive chops, and I believe he dragged around the same 4-string J-bass his whole damn career.
In general, if I even see 5 strings, I’m usually thinking “uh-oh.”