If a shop is plugging tires, they're old school. To my knowledge shops aren't allowed to plug tires anymore.
That said, I've used boxes of tire plugs over the years. The odd 1 here or there may leak, but if given the ability and tools, I'd plug a tire on the vehicle before changing it on the side of the road.
I'd plug a tire at home unless the tire won't hold a plug.
Reminds me, just plugged a tire on a car we bought a couple weeks ago. Found a screw in tire the night before my wife and son were leaving x country with it. No tire shops open at 9pm or 4 am!
But I need to get more, only got 2 left!