I have heard that this is how they break in some racing engines, and I have used similar techniques to break in my own (good results too).
Outside of engine break-in or 2 stroke engines, I have always thought the idea of "blowing the carbon out" was a myth, doubly so now that everything is fuel injected and computer controlled.
When I worked at the dealership we had a chemical they would suck into the vacuum system using a special tube and bottle adapter. The idea was that the chemical dissolved the carbon so it could be burnt/blown out when it is run. I don't recall what it was, but at the time the mechanics told me it was the same thing as seafoam. The adapter was just a valve with a straw on it so you could slow the flow of liquid down to get good mix with the air it was sucking in too.
They would start the jeep, pull the vac line off the brake booster, and then stick the hose end onto it. Then adjust the valve on the bottle so the engine ALMOST stalled, once 3/4 of the bottle was used they would just shut it off while everything connected. They would let it sit for 10 or 15 minutes, while disconnecting the bottle and putting the vac hose back. They last little bit of the fluid got dumped in the gas tank (just like seafoam).
When they started them up again, they didn't always fire right up, but after a second or two they would start and then they would smoke while running like you would not believe. The smoke from those vehicles would fill the whole shop in a heartbeat if they didn't hook them up to the exhaust system.