Use this knot when you need to tighten a rope to hold something down like a tarpaulin or to secure items in the back of a truck. I used three to hitch up and tether down my rain gutter. Click on images for larger images.
This knot can also be used as a crude pulley system with a 3:1 advantage if you ignore the massive amount of friction. I did this when I hitched up the HPS light in my growroom.
There are a few versions of the trucker's hitch, all of which are concerned with how the loop in pic. #3 is formed. One version uses a figure-of-eight loop, another uses a slipknot. I prefer this version because it's easier to untie. There's no knot to jam, the twist simply untwists when you untie it.