I've always backed in for the same reasons everyone else here says. It's easier to leave, better visibility, and after my tail lights got stolen I try to find a wall or pole to help stop the tailgate getting opened.
Either when I get down to 1/3 full or once a week, whichever comes first. It's usually tuesday nights after work. Big outliers being if I've driven a lot for work, or if the family's taking a day trip somewhere. That 1/3 is enough of a cushion to get me on my way if I have to get going somewhere...