There is not one "right" answer on that question.
It depends on each user personal preferences and experience. If you ask for your own use, just give it a try. Than you will see what suits you the best.
The main problem will be to "change the habit". Often, such feature can indeed be an improvement in itself. The problem can occur during the implementation. If you have someone who worked many years with the taskbar on only one of the two screens, the change can be quite hard for him. The benefit will be lost and, even worse, the productivity can even drop.
So I would be careful with such a change. I would let people try it first and then let them decide. Don't push them to use it "because it's supposed to be better"...