I play A LOT of disco and had to get a 5-stringer pronto as soon as my beginner's fretting hand became able to tackle one!
Disco relies on octaves - at its most basic, you will have the same note repeated several times, but the first time it will be, for instance, a low D, immediately followed by two high Ds, then another low D, before changing chord and moving on. You simply can't do that properly on anything other than a 5-stringer.
Quite apart from disco, there are rock and pop songs which rely on octaves; the reason why I'm hoping one day to buy an upright 5-stringer is that transposing for the normal upright often ruins the effect completely.