Some confidence that the brass stays in it's correct position, repeatedly, on the breech face until the ejector does its job, without falling down or moving to some other location, without the magazine follower assisting the process. I fully understand that the test doesn't reflect any condition I'd ever be operating the pistol in.
To be devil's advocate - does me running this test cause a problem?
I don't know about you but I function test all my firearms with the weakest and strongest loads I run, at angles all the way from normal upright shooting to upside down and everything in between. Also with the firearm brought to snow temps, with snow/mud in the mags, limp wristing WHO, all combinations I can think of. I don't have a large firearm collection but I don't put one on "forget" mode until I've done all this.