You are not wrong.. the "only" reason to buy the cable is because yours is busted..

Already having tuned my coupe with the DIY home kit did not net me any discount for the wife's roadster's tune short of the shipping cost. So they got to send my second cable for that "savings" difference.

You "could" use the cable with the software for the data logging.. but I have Torque Pro and haven't even looked into what their program offers.