Quitting iPhone apps as a habit

I've noticed more and more people around me habitually quitting iOS apps on their iPhones. They  will quit every single app until there is nothing left in the task switcher.

As far as I'm aware, this is rather unnecessary but maybe there are some reasons that people have that I'm not aware of. Is it trying to clean everything up? Is it to combat performance issues?

If you know anything about this then get in touch and let me know. Hopefully we can improve lives together.