That's sounds like its running in the background until I open it again. But in the same hand not sure if I'm fond of it doing that. Could lead to battery consumption.
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That is a very good concern, but it is not valid.
In Windows, for example, when you minimize it, it is running in (almost) FULL force, the only difference is you can't see it. It still requires RAM, CPU, etc.
For Android, when an app is 'minimized', that isn't the case.
All apps use two primary methods of getting things accomplished: Services, and Activities. Activities are the screens that you see. For example, the web browser. Services is are tasks that are completed, regardless of the activity. So when you click the download link in the browser, the Browser Activity is then sending a message to start the Download Service. When you minimize the app, the Browser Activity is frozen in time and will no longer consume CPU cycles. The download, however, will continue until it is done.
So if you are watching an HTML5 video in the browser and you minimize it, you will notice that the sound stops. That is because the video is not being done by a service, but the activity. The activity cannot consume cycles if it is minimized so the system will not allow the video to continue playing. This is a very strategic design decision to save on power consumption.