If killing task makes your phone run smoother then you have an app that is supposed to be running in the backgroud, but is not coded properly and is staying in the foreground. And in all actuality you want apps that you frequently used staying in a ready state in the background so that they open quickly and have the resouces available to them when they are needed. I'm curious what people actually mean when the say "my phone runs smoother". Do they mean the screens scroll faster? apps open faster?