Using RAM in Android isn't a bad thing unless you're experiencing performance issues. It's not really the same thing as in Windows, where it tries to use as little as possible. Android uses RAM that it doesn't "need" dynamically to support background apps, storage management, syncing, prefetching and other processes to provide a smoother experience as you switch between apps and other parts of the UI. In Android it's more accurate to think of it as you want it to use as much RAM as it can while still having enough to easily accommodate whatever you're trying to do, if that makes sense.
You don't need to kill apps unless they're going rogue and RAM handles itself, interfering with it is actually more detrimental to the system than just letting it handle processes dynamically. In 2010 it was important, a little, to keep an eye on RAM and CPU management, but in the 2013/2014 world of devices you shouldn't have to ever even look at it unless something is specifically wrong that you're trying to investigate. It's not going to help battery life, speed or fluidity to micromanage it manually or to let an app micromanage it.
Essentially, the OS is programmed to use memory dynamically and close unneeded programs automatically as needed. It does this so that as you switch between apps, they open more quickly and it also completes background tasks while RAM is not needed for user facing functionality. The entire purpose is so that things happen more quickly when you open an app, switch screens, switch between apps and/or use shortcuts via the navigation and notification menus. In previous versions, before the end of 2011, Android was not as good at this dynamic multitasking optimization, but since then it has come a long ways to where it is much better at these processes than users can hope to be doing things completely manually. Our intervention is usually actually slowing the system down, unless we're fixing something that is misbehaving.
Manually or using third party software to systematically override this optimization means that the system has to "rev up" more often, basically every time you switch directions in the OS. Just like in a car, you get better gas mileage and less wear and tear, plus overall better performance from keeping your RPMs in an optimized window on the tach, this is the same concept, but has much more attached to it. If you are manually closing an app or two in order to troubleshoot an app that is misbehaving, then it makes sense, but otherwise it is better to let Android do it's thing.
Using RAM isn't a bad thing in Android. Android dynamically assigns memory to apps as needed and closes them as needed in order to keep things as fast as possible. Force closing apps that aren't misbehaving is actually worse than just letting things run as they should.
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