You don't need to, but it might not be a bad idea. There's been guys who have issues with the crank snout breaking off that's probably more related to the added tension of a supercharger belt, but I figure that vibration will only add to that.
thats what I have heard before that the tension on the supercharger belt puts stress on the crank snout and the factory harmonic balancer is weak and if that goes, your engine is gone..
That does make sense, generally there is just more stress on the front bearings though but as long as you don't tighten the belt to a point where it cant even move up and down you should be fine.
I didn't and I was throwing belts. With all the money I spend on belts I could have bought a SFI balancer. I ended up with a professional products SFI balancer with a steal spacer ~$150 shipped.