I usually ignore these discussions on closing apps - but I do get kind of tired of hearing that it makes no difference whatsover. I know that iOS is supposed to manage available ram and free it up on the fly as needed - but I'm sorry - it doesn't always work out the way it should. Those of us who still use original iPads with iOS 5 know this. It's not a placebo, it's not to make myself feel nice. It's the fact that there are times my keyboard lags while typing an email 3 seconds behind my fingers - until I manually force close Safari - and bam - my keyboard keeps up again. No location services running, no music or movies running in any of the tabs... iOS just doesn't release memory aggressively enough on devices that lack ram - which would be the iPad 1, in particular.
I've got several (very good) games that I can't even open if I don't force close the last 3-4 apps first. And I've got some (again, very good) games that you couldn't get past about the 7th mission without it freezing up if you didn't close *everything* *and* shut down notification center.
So yeah - I get how iOS is supposed to free up resources on demand - and it's good enough at it that I don't worry about it often - not nearly as often as I have to with my work issue android (4.1), which routinely goes through 50% of its battery in a few hours. But it definetly is an issue for some devices, and closing background apps *does* have an impact on how the system runs.
That said, those of you running newer devices are likely to never see the effect - but stop suggesting that it can't possibly be the case for everyone. Because its not.