I wanted the ability to turn off my warp drive so I can save power. The only time I use warp drive is, you guessed it, warping. The rest of the time it's still running, chewing up power. That can add up. So I want to turn it off when not in use. You could even make it so the warp drive needs to recharge if power was turned off if you want to add to realism. Well you know what I mean.
