It a habit that we iPhone users do - closing the open apps on the phone.
According to this article by Maxwell Zeff / Gizmodo it does nothing to improve the performance of the phone.
This performance myth that has been running since 2007 - after it was posted on an Apple Forum site 1 week after the original phone was released.
So this compulsive thing we do is not actually needed.
It’s one less distraction in meetings.
https://qz.com/stop-closing-your-iphone-s-background-apps-1851269132