I've seen these used in low income homes where the basement electricity is paid by the landlord for coin operated washers. Then someone gets their electricity cut (lack of payment) so they use these cables to jump the outlets and steal electricity from the landlord.
The dude just went to a hardware store and bought an extension cable and a replacement plug head. Snipped the female end and added the male in like 5 minutes.
The only practical usage of those things is jumping a generator to a house during a blackout.
Edit: yes please bring on the down votes for me sharing a story about how the poor use these scary cables. Real nice.