I would think, although I'm no expert in this field, that most "battle" armor in the middle ages was functional. In any case, look at it like this. If I was a foot soldier in the 10th century and I was lucky enough to have any armor at all I would want my armor to be functional!I was looking for some medieval armor suits that are really beautiful with all kinds of decorating. They dont have to be practical in combat, ceremonial armor suits are fine too. I have a fiery discussion with a friend about how boring the armors in the games are and I want to show him that there are real armors that are beautiful too!
That said there have been some finds of exceedingly ornate armor that appears to have been used in battle. A number of years ago a guy in England made an astonishing find of Anglo-Saxon armor that had been buried (and never picked up) after a battle and was decorated with more than 5 kilograms of gold. Nothing boring about that.
Much of the ornate armor you see in Europe in museums these days is from the late middle ages. Much of it is also specialized jousting armor (refer to pictures above). It's really nice but not built nor intended to be used on the battlefield.