I am a 5 string player. Have been for years and years. That said, there are maybe 4 songs on our list that "need" a B string for lower notes, and a handful that use a low D. I have a 4 string P and a 4 string J and I have used them before for a set or two if it works out that I don't need the low notes. I will say a couple songs seem to feel better on a 4 string. I have thought about swapping basses mid gig or mid set, but then I get lazy. With my 5 and the 1/2 step drop on my Stomp, I'm ready for anything.
I do use my P and J for a couple side projects. Jazz gigs get the P with flats. Also use it for some singer/songwriter stuff. I'm doing another side project that's the Weezer "Blue" album front to back where the J tuned Eb works great.
It's nice having options, but when push comes to shove, I grab the 5.