With ordinary appliances you can be fairly certain they're safe if you pull the plug. With a gizmo that taps a wireless power source in your house you can never be.
If for some reason you want to do something to a device that's less than safe if it's plugged in you run a risk. If you want the device to be guaranteed shut off. e.g. because you want to clean it under the tap, or because it overheats (potentially causing a fire), or because you want to screw it open, you may have a serious problem.
If you want to ensure some sneaky piece of hardware (like a "smart" TV set with voice command operation) is really off
As I've noted before, in this age of networked machines, the real issue is control. Who controls a given piece of hardware? You or the manufacturer? The manufacturer has several ways he can monetise control over an application. Ranging from privacy intrusion to enforcement of policies.
Most ordinary people, good little consumers as they are, have already lost this contest. Their "smart" hardware can be under manufacturer control for all they know and may phone home and collect and transmit personal ("anonimised") data back to the manufacturer as that manufacturer sees fit. This basically applies to anyone who uses a smartphone, a recent car, or any kind of networked piece of electronics in "consumer mode". Only people with interest in (and expertise in) hacking and controlling their stuff can retain control.
It will also allow the manufacturer to enforce all kinds of "policies" on the user of that appliance. E.g. a printer will stop printing when the ink cartridge tells it the allotted number of prints has been reached. Regardless of how much in is left in the cartridge. Or a "smart" espresso machine that refuses to work with any but the manufacturers own coffee cups. Or a console will refuse to play a non-authorised game. Several e-readers will refuse to display files that aren't on "allowed" servers, plus they will tattle about what you read, when, and for how long. If you're unable to run Wireshark on your home network (or simply lack the time) you may never know.
This cordless plug is simply the next step towards a world where individuals' control over their home and the stuff in it is diluted and either off-loaded to whichever party thinks they can monetise a little piece of control over your personal surroundings, or routed through some piece of electronics that exercises actual control instead of the appliances' owner and balk in an emergency.
If I want an appliance to work, I'll find somewhere to plug it in.