It's a well known remedy for those who are desperately clinging to the last few ounces of juice in your dying battery. Shut down any apps you've let open.
However it's now been confirmed by Apple that this has absolutely no effect on your battery life what so ever.
As was first published in 9to5Mac, an Apple customer emailed Apple CEO, Tim Cook to find out for sure if a) does he quit his iOS multitasking apps frequently? and b) is this necessary of battery life?
Apple's iOS Chief Craig Federighi responded to the email with a succinct and polite response that dispelled the myth forever.
As 9to5Mac further explain: "On a technical level, most of the apps are either frozen in RAM or not running at all, the system just displays them as a history for consistency. This is why the battery life impact is negligible."
So there you have it. Straight from the horses mouth. He didn't say anything about lowering the brightness of the screen though so we're going to keep doing that until we're told otherwise.