NCC320, you are SO right on. I removed the topping lift from my boat as soon as I bought it. It's just another line to get in the way. It's not a sail control and if you have a solid vang (which I highly recommend) there is just no need for the topping lift.
I have to disagree with sailingdog on one issue however. In very very light conditions the main needs to be made as flat as possible to try and squeeze as much power out of the breeze as possible. In these conditions air flow has a very hard time staying attached to the sail. Detached air flow means loss of efficiency and power. A flat sail allows the breeze to maintain nearly complete flow attachment for best sailing performance.