Campy traditionally produced only road racing gear with a fairly narrow range of cassettes. Back then you'd lose all your cool-points if you had anything bigger than a 25 on your cassette. Now with options ranging from corn-cob to 11-29 Campy has a knuckle screw.

My experience with an unadjusted B-screw is that on bumpy terrain that chain will wander and even walk itself up the cassette. Which is really weird to see, riding along and watching the gear indicator climb up from 5 to 9. Bike was new and I was dumb enough to ride it as shipped without checking that. Got home, adjusted the B and all was well for the next year or so until I killed that der.