1. use charged attacks with both weapons simutanously
2. increased attack speed
3. different weapons such as blunt, blade, and spear have different affects on armor
Those would logically be the three biggest advantages to it. Your third point is vaguely confirmed, with mace perks that ignore armor and axe perks that cause the character to bleed out. We don't know much about the overall perk system yet, but I would imagine it goes deep enough to give tactical meaning to dual wielding specific combinations of weapons.
I don't think your second point has been bluntly confirmed, but I imagine the attack with your second weapon would come in between the full animation of your first attack. For example you have shortswords in each hand. You swing and strike with the first one. Just as it connects you swing with the other one, and as you're pulling back your first wepon the second one is heading for the target. That seems to make sense since it has been confirmed that if you have dual fire spells on each hand you can send a stream of rapid-fire, fireballs at the enemy by alternating back and forth between each hand.
The first point hasn't been confirmed at all(as far as I know), but that would be great. I think, at the very least, we'll see some of that in the finishing moves the game offers.