iOS multitasking bar is better regarded as a browser history and not a task manager. With that concept, everything will fall easily into place. Fraser, in his blog post, explained that the misconception of iOS multitasking bar draining battery life has been going on for a long time. However, it is far from the truth since, like we said, the iOS multitasking bar is just a reference for the user to switch between his recently-opened apps.
Fraser supports his thesis saying that if you reboot your iPhone, you will still have all your recently-opened apps in the multitasking bar.
In an attempt to clarify how the whole iOS multitasking bar works, Fraser has composed a 16-min video showing apps running on an iPad in different states ranging from active to inactive and everywhere between.
The video is worth every minute of your time for it provides a comprehensive demonstration of memory usage on iOS killing by that all iOS memory usage misinformation.