Ask an Aran thread.

It is just easier to do overswing after overswing than to perform a Final Blow. Final Blow really doesn't mess back knockbacks, but it can be a hassle to use if you don't do it perfect every time (i.e. you press the key too early and you lay down for a second). I only use final blow now to finish off a mob because it can sometimes save me a few overswing hits. And as a warning, Final Blow's range is WAY TOO FAR. Whenever I am training I have to be careful to not hit things too far away because then I aggro them, have to rush to them, and I take a lot more damage. And just cause I feel like adding it, the picture in my post illustrates my best reference point for Final Blow's range. From one of those platforms to the other.