Kirk McElhearn argues that quitting an app might not speed up your iOS device, but it might make a difference to your battery life.

There is definitely room for improvement in the information Apple presents on background apps. As is, all you get is binary information, a scrolling list of apps that are running, in some form or another. At the very least, some kind of indicator that tells you that the background app is partaking in some battery sucking activity would be useful.