As far as I'm concerned, you always point the muzzle in the safest direction, and that's not necessarily always down.
According to Jeff Cooper's latest commentaries, he prefers the standard rifle ready position, with the butt at the belt and the barrel up at a 45* angle to the "tactical" ready position, that is, the butt in the shoulder and the muzzle down. He says the latter would tire one quicker, which seems to be true.
If you're, for instance, standing on a concrete pad out doors, it's probably safer to point your muzzle up than down. Same thing if you live on the top floor of a building. Point the muzzle in the direction it's least likely to do any damage in should you initiate a negligent discharge.
Nightcrawler- TFL Alumnus