Gregor
Lord of Altera
To clarify, Plate provided extremely good (close to perfect) protection against cutting weapons, which had been standard sidearms for centuries. In addition it was pretty good at deflecting spears and unaimed thrusting weapons, as well as early projectile weapons. A user of plate really only had to worry about blunt crushing weapons, extremely close range combat (wrestling), and powerful projectile weapons (crossbows or longbows) at short range.
With the advent of plate on the medieval battlefield, both the design and techniques of swords began to shift to handle the new threats. Two-handed weapons became more popular as the shield was discarded. Swords often became longer and thinner.
You can see on the picture i posted how people used swords.
People used their swords for half-swording, where they would grip the sword by the middle of the blade in order to thrust through the gaps of his opponent's armor. You can see the man on the left going for a thrust, while his opponent is employing the mordschlag, where you take the blade in both hands and bash your enemy over the head with the hilt of your sword. Every part of the sword is dangerous in the hands of a proper swordsman.