On iPhone the animation speed was/is there to help give apps time to launch, for example, so while the app is launching you see the animation and it hides the fact of the app launch time. If you disable the animation / speed it up, sometimes you run into apps that you notice are unresponsive until they have finished launching. You can’t disable the animation completely, but you can reduce the animation time to as low as it can go. This was a while ago as I haven’t been jailbroken for a few years now. What I describe above is my experience with “disabling” the animations.