The principle is very simple and yet sophisticated, one hand is always helping the other hand, two moving weapon is always better than one, first hand holding the weapon can do the blocking while the other weapon will pursue to strikes.
Every movement of your partner will always have gap, the gap can be your opening to execute your attack this will be a great advantage to you, because he will be distracted to two weapons doing the block and strikes at the same time.
In addition to your training you will also going to build your confidence that will help you in crucial situation to keep and maintain your distance away from the center line of your opponents range.