I've never personally tried them, but I think they claim that on the bridge pickup your since your middle strings are closer to the bridge, and the higher and lower strings are further away, you get a bit more fullness on the lows, less ice pick on the highs, and a bit of twang from the middle. The neck is the opposite, middle strings are closer to the neck and fuller, bass and treble strings are further away so a bit brighter and less muddy.
It might all be B.S. Idk...