They were probably put there to prevent the #1 case of injury in a lightsaber fight which is the loss of a hand. Look at how many of the fights had someone slide their blade a little to de-hand their opponent. You gotta hand it to the sith on their ingenuity.
Good to know the mindless drones of Middle America will once again be flocking to the theaters to watch another gay and dumb FALLACY OF A MOVIE circa Christmas of next year when Star Wars VII comes out. I for one will not be going. I will not see that movie.
It's sci fi, it's just there to look cool, no need to bring logic into star wars, if so we can pick apart so many other things that you loved about them so much. Besides, it may be a hand guard, it may not, we don't know everything about it.