The "E" has some applicability in the field, if you have bumbled about in the woods, snow, obstacles, etc. It is also a good idea when you take a gun out of storage and get ready to transport it - the cleaning patch incident described above would have been caught, for instance. On the dark continent, some bugs will build mud nests in your bore overnight. Some old PH's closed their empty actions and dropped a cartridge nose- down in the bore. No bug could get in, and they had one ready round to hand!
But at the range, unless you suspect an anomaly in a round fired, all looking down the bore from the business end will do is excite everyone around you! Most of us shoot some form of repeater - revolver, semi-auto, magazine fed bolt, pump or lever guns. In order for the gun to function as a repeater, you will have to load multiple rounds, and discharge them repeatedly. You can't be doing ACTS PROVE between shots in a repeater.
Long before the latest trash gun laws, responsible shooters opened the action of a firearm which was to be left unattended, on cease fires, and before going down range, or when handing it to another shooter. If there are rounds in an attached magazine, (think tube) it is courteous to so inform the individual receiving the gun. (It is not always desirable to cycle a pump or lever gun to empty a tube, when the receipient is about to shoot it anyway!)
Allow some common sense to infiltrate your gun handling. Don't allow our muzzle to cover anything you are not prepared to destroy, and keep your finger out of the trigger guard until your sights are beginning to bear on an intended shootable target. And, unload it before you set it down, and open it before you offer it to someone else. That's about got it. Kept millions of shooter safe on ranges for decades before the guvment dreamt up ACTS PROVE!