Originally Posted by heartcolorgrey
What everyone says here is true about uphill/downhill.
The only time 1st/reverse is NECESSARY though, is when your e brake is worn down (be it from doing dumb stuff in parking lots, normal wear and tear, etc). Even then I would just get the e brake repaired.
Turning wheels into the curb is always a good idea though.
Yeah, E-brake + turning wheels so your front tire hits the curb if the brake fails is where it's at. Leaving in gear is an added safeguard against your car rolling away and doing damage.
As for what I do when not on a slope, I always leave it in the gear I plan to use when starting the car next (as some others mentioned). Honestly, this being my first car where 1st and reverse are right next to each other, every once in a while I'll think I'm in reverse when I'm actually in first, or vice versa. Thankfully I tend to ease out of parking spots...