to keep it simple, the extra boost MAY push the piston open (if you fitted the dv backwards) and it can cause premiture opening, and also slow closing time ie
the valve opening on its own or after opening it not closing propperly.
although some guys have found the softer springs better than the stiffer, each car, map and set up is diffrent so some times best not to be a sheep
i know of a TT near me who is stage 1 he had to use a yellow spring and a spacer shim so it just under the strenght of the blue (i think) yet i dont think my valve will open with that set up lol
another good tip is to remove/bypass the N249, this could stop any premeture opening... again some cars dont like it.