thanks, but i think we would agree that if a hand soldering iron, at 400degc, was pushed against a PCB covered in solder resist, then when you remove the soldering iron, you can see where the solder iron has been...since the solder resist wont be smooth any more, it will be deformed (possibly my use of the term "melting" was inappropriate)
Now suppose that we are trying to hand solder a component to a pad that has a solder mask oversize of just 0.15mm.....then we can see that the solder tip may inadvertently touch against the solder resist near the pad, and impinge on the pad a little bit (the deformed solder resist may find its way onto the pad)...making the pad harder to solder.