Originally Posted by spinner

The mechanical advantage of a block and tackle system is easy to calculate. If you take the number of lines running into and out of the moving block( in this case the loop) that gives you your theoretical mechanical advantage. In the truckers hitch case, 2 lines(one in, one out) gives you a mechanical advantage of 2. In reality, it is less for several reasons. The bend the running line makes passing through the loop is much less then the minimum bend usually recommended for block and tackle systems,the larger the radius of the bend, the lower the friction . The friction of the rope sliding on itself is high, in fact you can quite easily wear right through the loop if your pulling a fair bit of rope under some tension. This is fairly common, particularily with synthetic ropes. All that aside , the truckers hitch is a very useful hitch. IMHO, the bowline and or figure of eight , clove hitch and sheet bend, along with the truckers hitch should cover most of your knot tying needs
Cheers