Greybeard and Range, you are BOTH right. Shooting a scoped/sighted rifle, the TRAJECTORY has an arc. Conversely, if the barrel is level to the horizon, the bullet begins dropping the milli-second it leaves the muzzle. Many guys have a belief that the bullet rises after it leaves the muzzle. They are not taking into consideration that the barrel is not held level when shooting.
OK, ANYWAY~ I used to shoot competitively and knowing YOUR rifle is the best way to begin your scope to target alignment. FWIW, without causing any further arguments (as this original post was supposed to be for opinions and experiences), I begin my centerfire rifle shooting at +/- 20 yards. I learned this trick from a retired gunsmith. In MY EXPERIENCE, it is absolutely accurate - depending on your caliber and load. I zero at 20 yards and I am zeroed again at 250 yards. Depending on caliber and load, bullet weight, etc..this is what works very well for ME. If I have time to hit the range, I just set up at 150 and pop a few rounds. I know I can easily shoot out to 300 yards with no hold over for my hunting set up. (.270/130gr.). This is all on a perfect 65 degree day with no wind, of course!!
The point of impact at 150 yards is 3" high and the point of impact at 300 yards is 3" low. Us men all know that 3" isn't very much.....(!) Put the reticle on the center of the chest behind the shoulder and squeeze. Instant venison.
Again, depending on your caliber and load, this is really accurate. I found that the .223 Rem, .270, 7mm Mag and .300 WM are nearly identical in trajectory out to 300 yards. The exception is the .300wm hits about an inch higher at 300 yards. Go ahead, try it out!! You will be surprised.