When I notice someone force quitting apps on their iPhone, I now have the perfect resource to point them to; especially this little nugget in the footnotes:
The other contributing factor to believing that force quitting is good for your iPhone are the handful of apps that have been found to be repeated abusers of loopholes in iOS, such that they really do continue running in the background, wasting battery life. Most infamously, Facebook was caught playing silent audio tracks in the background to take advantage of APIs that allow audio-playing apps to play audio from the background. They called it a “bug”. In those cases force-quitting the apps really did help, and I see no reason to trust Facebook. So if you want to keep force quitting Facebook, go right ahead. But don’t let one bad app spoil the whole barrel. The Battery section in the iOS Settings app can show you which apps are actually consuming energy in the background — tap the clock icon under “Battery Usage” and don’t force quit any app that isn’t a genuine culprit.