Is dual wielding (like two swords, a sword and a knife or two knives) an actual effectiv fighting style or just something that looks cool??
With two swords, not really. There’s a few stray examples. It’s not so much ineffective as incredibly difficult. With that in mind, you can absolutely learn how to do this as an exhibition technique. Which, yes, ends up in the range of something that looks cool.
A sword and an off hand dagger has a lot of utility. The off hand dagger actually becomes a defensive tool.This can range from something like a stiletto, used to deflect an incoming strike, or it can include a swordbreaker, which depending on circumstances might simply hold your opponent’s blade in place while you turn them into goulash with your sword.
It’s probably worth remembering that the parrying dagger is more common when dealing with lighter blades, while sword breakers were more common when dealing with heavier, slower, blades.
Dual daggers are a legitimate, hyper-aggressive, knife fighting option. You’re trading any kind of defense for more opportunities to attack. When the user has the element of surprise it can make a bad situation so much worse, but if their foe can respond, it can go wrong for the dual wielder very quickly.
If you’re wondering how a knife can go from being a defensive tool to an offense option, it has to do with the ranges you’re engaging at. Incidentally, a swordsman with an off hand dagger does have the option to attack at extremely close ranges where they can’t attack with their sword.
I know we’ve said this before, but weapons have specific ranges. Get too close, and you can’t use them anymore. A sword works best at a little over arm’s length. For example: A sword won’t do much good
while you’re lying on top of your foe. On the other hand, if you can reach out and touch someone, knives are always good to go. The advantage for a sword is it will add 36-40 inches to your reach.
It’s also worth remembering that a sword with an off-hand pistol was a real option up into the 19th century. You’d open an encounter by putting a bullet in someone, and then use the sword.