One of the biggest mistakes on the iPhone doesn’t look like a mistake. In fact, it looks helpful.

But potentially millions of people are wasting time, battery and finger energy on an entirely unnecessary and perhaps unhelpful exercise, every single day.

iPhone users are busily swiping away apps to force them to quit when there is no need to at all.

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Experts have warned yet again that there is hardly ever any need to force quit apps – done by double tapping the home button and then flicking the apps up and away – despite the fact that it is common practice.

The latest round of warnings came after Apple pundit John Gruber wrote warning people that there is no need to flick the apps away. But Mr Gruber pointed out that he was far from the first to do so – with warnings going back to at least 2012.

The practice of swiping away apps is based on a misconception about how iOS works on iPhones and iPads, he said. And not only is swiping away apps unnecessary, it might even be counterproductive.

People might presume that it’s important to quit apps to stop them taking up memory or battery while they are sitting in the background. But that’s wrong.

“The iOS system is designed so that none of the above justifications for force quitting are true,” . “Apps in the background are effectively “frozen”, severely limiting what they can do in the background and freeing up the RAM they were using. iOS is really, really good at this.

“It is so good at this that unfreezing a frozen app takes up way less CPU (and energy) than relaunching an app that had been force quit. Not only does force quitting your apps not help, it actually hurts. Your battery life will be worse and it will take much longer to switch apps if you force quit apps in the background.”

When an app is swiped away it is forced to quit, meaning that it must open up from scratch the next time it’s launched. That in turn means that it has to perform all sorts of intensive operations that otherwise would have been avoided if it had just been left hibernating, and the iPhone uses the battery more as it does so.

Even Apple’s most senior software executive, Craig Federighi, has tried to shut down the fashion for swiping away apps. Last year, an iPhone user emailed Mr Federighi to ask whether he swipes away his apps and if it is helpful to do so – his reply only read “no and no”.

But the advice didn’t seem to spread and many people are still swiping away the apps.

There are some times that it’s helpful or even necessary to force apps to quit, and that’s presumably why Apple leaves the feature in the iPhone. If an app crashes and is hanging, for instance, it can be a useful way to restart it; other times if an app isn’t working properly, like being unable to connect to the internet, restarting can be a useful way of waking it back up.

Apps also sometimes abuse the privilege of running in the background on your phone. Facebook, for instance, was found to be using tricks to keep itself running fully in the background and so consuming battery, Mr Gruber noted, and in cases like that it might be sensible to quit apps. Users can see which apps are using more battery than usual in the battery option in the Settings app.