The whole idea of a diff swerve is that you have 2 motors, but depending on how you drive the motors, you can send all the power from those 2 motors to the steering output OR to the wheels output OR to a combination of the two.
In a normal swerve module you need 2 motors, one for steering one for the wheel. But the power from the steering motor cannot be redirected to the wheels or vice versa. The wheel motor drives the wheels, the steering motor just steers.
As it turns out, steering is a low power task (most of the time at least) so if you can sneak power from the steering motor into the wheels, you are in a better position (potentially).
One thing that I regret is that this design took soooooo looooong to get done (and it still isn’t done done). Once FIRST moves to 20 slots on the Power Distribution Panel, a lot of the impetus for Diff Swerve is gone. You could just add a 2nd motor to the drive wheel (using 12 motors for your drive is crazy when you only have 15 available – using 12 when you have 19? Well that isn’t 100% crazy – maybe only 75%, right about my level of crazy )