So, here I am, perusing posts from before my time, and I found that nobody has anything to say about double purchasecounterweight fly systems. I work in a hemp house, and have only operated a double purchase once. It was great! However it requires twice the weight and twice the travel of the operating line to move the scenery because of the 2:1 ratio. That is my vote.
Some lighting and sound folks may not think they need to be concerned with fly systems; wait til you work in a hemp house or a place with no chain motors. My ME, for every show loads pipes that weigh upwards of 500 pounds sometimes and he gets them in the air. We used to bull them out with the whole staff- now we use a block and fall. It takes longer, but it is much safer!