There is no off balance without first having balance. The key to effective kuzushi is to be able to cause an imbalance in Uke while Tori maintains his own balance initially and throughout the technique.
If Tori is off balance it does not matter what kind of kuzushi is applied on Uke, the technique will be weak, clumsy and ineffective as power is not correctly focused and controlled.
Balance and off balance here can be both physical and psychological, they often work together.
Just my thoughts.