So that you can roll them down and don't need to run the air-conditioning/heating all the time? Examples: 1. Good weather, sub-freeway speeds. Large parts of t

So that you can roll them down and don't need to run the air-conditioning/heating all the time? Examples: 1. Good weather, sub-freeway speeds. Large parts of the US (and the world) have good weather for most of the year. 2. Going uphill in hot weather, where running the AC would put too much strain on the engine