I use plugs to get a car back on the road for a day or week or two. A nail hole in the tread should be no problem (normally) for a plug. I use plenty of cement also... needed or not. I do pull the tire when I can shortly after the flat to get a patch inside at a tire store. They cut the plug close to the casing and install the patch. Also re-balance after the repair. As mentioned, there is some risk (slight?) air may leak between the plys. Also most of my vehicles may at some time get driven at high speed and the patch inside is insurance the plug may work loose.

My lawnmower on the other hand had a hole in the sidewall I fixed with a plug. No problems in 10 years I kept that tire.