Here is a little flashback story for probably many of you.
If you are, let's say, constantly visiting Facebook, Twitter and YouTube, don't you think your phone/tablet should have them ready for next time? If you are on Facebook, then manually close it down, you are just letting your RAM space sit there. It's just sitting there, collecting dust. Now if you need more memory, for maybe, Plants vs Zombies, your OS automatically does it for you. It kills your oldest tasks, then goes to your most recent, and so on.
If you're to lazy to read, what I'm saying is when your apps are being closed out automatically/manually, you're wasting free RAM space. Just don't worry about it.
Sorry for no source, I forgot where I read it from.
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