The Recent Apps list is just a convenience for you--it allows you to switch a little more quickly between apps that you probably use often. As discussed above, it is not a way of "closing" an app--the example I always use is Pandora. If you start playing music with Pandora, then swipe it away in the Recent Apps list, the music keeps playing, meaning you didn't close it.
In Android, you don't have to close apps, because the system prefers to keep its RAM relatively full. If it needs more RAM for a newly opened app, it will close an unused app on its own. I'm not an expert, so if you want more details, check the many articles on the web about this, starting with
Multitasking the Android Way | Android Developers Blog
That's not to say that an app will never misbehave. If the system is getting laggy, you can check using various apps like this one
https://play.google.com/store/apps/details?id=com.lookout.zapper&feature=search_result#?t=W251bGwsMSwxLDEsImNvbS5sb29rb3V0LnphcHBlciJd to check on how much CPU your running apps are using, and force stop any that seem to be using an inordinate amount.