[quote=Legion X51]
No, no, no, no, no, no, no!The point of plate armour is not just to strut about in big fancy suits of heavy metal sheeting. Plate armour, as in a proper suit of plate armour, will deflect the blow from a mace or warhammer quite well, but it's not the 'plate' that deflects the blow, it's the padded gambeson and leggings, as well as things such as the mail hauberk that you wear 'beneath' the armour that protects you from a mace, club, warhammer or any other blunt instrument of war. Arguing that being in or being out of plate armour, when you're being hit by a mace, doesn't make a difference is folly. You would be much, much safer and much better able to continue fighting if you were in plate armour if you were hit by a mace. In fact, I would argue that a sufficiently-crafted set of plate armour (styled in the form of Greenwich armour, Gothic or Maximilian) would be able to shrug off blows from maces or hammers without too much of an issue - after all, there are numerous examples of Gothic and Maximilian plate being able to deflect musket bullets from as close as 20 yards away.
[/quote]

That just isn't true, at least not for the majority of cases. Perhaps it is possible for an expensive, specialized suit to be made specifically for the purpose of mitigating blunt damage, but one of the most attractive uses of maces and other blunt weapons was their effectiveness against armor. They could damage the wearer, thick armor, or both in a much more direct way than blades ever could. 

Reference: [url=http://en.wikipedia.org/wiki/Mace_%28club%29#European_Middle_Ages]

(Edit: that being said, if you're going to get hit, having the armor is better than not having it)