MsSnaka is hardly at your level Jerry, give the guy a break.
Recent example of why you should use it. Experienced engine builder in our local 'race shop'. Sends the crank out for grinding, gets it back on a Friday, race day Saturday morning. He HAS the mics AND the experience to measure the clearance, he thinks he doesn't have the time (foolish eh?). He drops in the crank to my FRIENDS race engine with NO measuring. I let him have it with both barrels, at the very LEAST use Plasti Gauge to see if it's in the 'ball park', which he did, and it was. He was trusting the machine shop to get it right, (I trust no one)!
If I was doing the engine I would have mic'd it AND used the Plasti.
As fate would have it, the used crank he selected for the build was wrong anyway and would not accept the flywheel. Race day didn't happen, other stuff happens when you don't pay close attention.
Richard Hudgins (JBL Cobras) uses Plasti Gauge and MANY other top notch race teams use it as well, as the FINAL step. It IS as accurate as the guy using it, which is also true with micrometers! EASY to make a mistake in either case.