The two outlets could be on different circuits, if for example one of them is connected to a switch on a lighting circuit.
Then, the cable will be powering one circuit from the other. A circuit limited to 20A could draw 40A before blowing, causing damage to the wires.
Someone might do some wiring work on the lights, and shut off the lighting circuit, and still get zapped (though most electricians would test it before touching it, since breaker labels are rarely accurate).
There are many creative ways to die to a cable like this.
The two outlets could be on different circuits, if for example one of them is connected to a switch on a lighting circuit.
While this is technically possible by cutting the bus bars linking the upper and lower sockets, this is a duplex outlet and by default both sockets are internally connected. It’s fantastically unlikely anyone would go out of their way to create the setup you described, which would also require by code for both circuits to be connected to a linked breaker so that if one is overloaded both circuits are tripped. Making one of the outlets switched would also create an extremely confusing situation for the user or building owner, which would inevitably result in a never-ending bitch session at whoever installed it in the first place, e.g. every time the cleaning crew plugs in their vacuum cleaner and this outlet “randomly doesn’t work sometimes.”
But then, if someone is running around with a ready-made double male mains cable in your building, all bets are probably already off.
Outlets where only one of the two sockets is controlled by a switch is extremely common for lighting in the USA.
