Peter is correct, they do mop and hold moisture and if they are sat on the sill they will cause early rot/corrosion. Better to lift it clear of the sill rather than remove it. It's there to prevent panel bounce, not sound proofing. Lift it to about mid-point and waxoil~ inside the panel while the card is removed.
I just got rid of them all together. Even if they are moved up the same thing will then happen to whatever they are attached to in the end. I was totally gutted when I found out about these things as my sills were solid 2 years ago, then last year at the MOT they found it to be quite crusty on the back sills and these were the cause.
My car has been garaged for the last 4 years of its life and very well looked after and I still fell foul. I guess you live and learn. I just wish someone had told me about these when I bought the car. Never-mind, at least I am now passing the message on to others.