After many years as a mechanic in EULL service station environment, I have plugged a lot of tires, and most, over 99%, have been fine. With that said here's a quote form the NHTSA tire brochure :
"The proper repair of a punctured tire requires a
plug for the hole and a patch for the area inside
the tire that surrounds the puncture hole.
Punctures through the tread can be repaired if
they are not too large, but punctures to the
sidewall should not be repaired. Tires must be
removed from the rim to be properly inspected
before being plugged and patched."
The best practice was taught to me by my dad, plug a tire and use it only long enough to get it replaced. For him, less than 2 days. For me, has taken longer at times due to financial concerns.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT