The iPhone Trick We ALL Do Is Completely Pointless

According to Apple Insider, the app switcher view does just what it says - it makes it easer for you to quickly jump between recently used apps - despite common misconceptions. You can prove this by rebooting your phone and then trying it again - the apps will still open, despite the fact that the phone has restarted. 

Oh.

The only reason to 'force close' an app would be if it's crashed, or is experiencing problems. However, there are some exceptions to the rule, as certain apps will keep running in the background (i.e. by tracking your location or playing music). It's easy enough to find out which apps these are - simply go to your Settings > General > Background App Refresh. From here, you can select which apps you want to keep running constantly. 

If you're worried about battery life, you can preserve it effectively by turning down your screen brightness or changing your battery settings to Low Power Mode. 

You're welcome.