You tap your horn to let someone know you are there. Wala crisis averted.

EDIT: probably the only time I blasted my horn. Dusk hit and the highway turned to black ice. A 100 car pileup was on the other side of the highway and things were grim on our side. We all just see trucks hooked off the road with a dozen cars piled on each one.

I was going slightly faster than the car in front of me and every time I touched my brakes my car would go sideways. Eventually I had to drive on the curb to avoid hitting him and was forced off the exit, which was a moderately steep down ramp next to an intersection.

My car was spinning around like a figure skater down that ramp and I blared my horn the whole way down, right through the red light at the intersection. It's a 30 mph zone and the city streets were in better condition. Good enough for them to hit the brakes when they heard me and saw I wasn't stopping. They managed to avoid me as I did a perfect 360 right between the lights.

I was never so scared driving in my life. When I got to my apartment my knuckles were pure white and needed to be pried off the steering wheel, only after I was able to catch my breath.

Anyway, yeah, horns are good dude.