[Sorry for the funkiness with the pictures - trying to transplant drawings from a smartphone]
Consider this arrangement...
The black lines are the ground connections between the components. The yellow approximates the current flowing in the wire. The wider the yellow, the higher the current.
If the ground connection ONLY is broken between the battery and the motor controller, you will have this...
The NXT cable and USB cable (and Samantha power cable) have to handle the return current for all the DC motors/servos powered from the battery.
If the Samantha is powered from the end of the Tetrix controller chain, it will be less of an issue as a broken connection is likely to take out the Samantha as well. But this creates the possibility for differences in the ground potential that *could* produce other problems.
With Matrix there is no power-out connection for daisy chaining: one controller, one battery.
I found the Samantha alternate wiring for Matrix document which highlighted the issue back in 2012.