I have and use Wilson case gauges for handgun (9 mm and .45 ACP) and rifle (.223 Rem). All .223 rounds are processed on a single-stage press; all handgun cartridges are processed on a Dillon SD press.
For .223, I run every hand loaded round through the gauge; if it "fails" but only barely, the base of the cartridge gets a dry marker slash and the round is still fired but the brass gets tossed afterward. Every failed round is always very close to passing (otherwise, I wouldn't even shoot it).
For the handgun calibers, I use the gauge to indicate how well the Dillon SD is producing cartridges. 99.9% of the rounds that "fail" the case gauge test pass a plunk test of my .45 pistols. So far, all 9 mm rounds pass; only some .45 cartridges don't pass. The ones that do not pass usually can be processed through stations 3 and 4 again and then they pass. So the case gauge just indicates which ones I process again.
I like knowing my rounds pass SAAMI specs. Is it critical that they do? No, not for what I do. I do believe that auto-loading rounds that still pass the plunk test may not actually feed well.