For me, a big drawback of extension ladders is that it usually takes a lot of effort to extend them to the desired height. This is partly due to the way in which they are rigged. Typically, the ladder is operated by a rope which is fastened to the bottom of the extending part of the ladder. The rope runs through a pulley at the top of the stationary part and back down to ground level for the operator to grasp. This simple arrangement is inexpensive to manufacture but it requires a force on the rope which is equal to the weight of the moving portion of the ladder. If the ladder is large, or if the moving parts have a high degree of friction, the ladder can be very difficult to extend when it is standing upright. This, in turn, makes it difficult to control the ladder and compromises safety.
I recently obtained an old extension ladder for free. Its rope was missing and while I was measuring it to find out how much rope I needed to buy it occurred to me that I could convert the ladder to a double-pulley system which would make it easier and safer to use.