Fair enough, but I'm sorry, in real life and what happens with my iPhone, when I have 20 Apps open, my battery drops somewhat quicker than if they weren't open (tested over a 2 day period) and when my Apps are "open" in the multitasking tray, JailBreaking it and using SBSettings, I have seen with my own eyes the RAM increase when I have closed down Apps . . . Still a good read though, thanks.
Yeah, but how much of that is a result of being jailbroken? My battery life has always been noticeably worse when jailbroken. Maybe there's something going on when jailbroken that interferes with the normal multi-tasking features. MacInWin also raises a good point... even though ALL the apps aren't actually open (note: there is a module for SBSettings that will show what apps are truly open), there easily could be some running, especially music and navigation apps that were very recently opened. But that really only applies if they are actively working in the background. If you pause your music, iOS will pause the app and eventually unload it if need be.
I'm looking at my list now. I have about... 98 apps in my tray. Yes, I sat here and counted them. 98. I forgot to charge my battery last night, so it has been over 24 hours since last charged and seen light to moderate use in that time, and the charge is about half. I'm going to scroll over to the 9th app in my list, which is an app that plays customized ambient music that I use at night sometimes. That was in a true paused state and popped right away. Number 11 is Slacker Radio and popped right away, so it was properly paused. Number 19 was another ambient sounds app... it had to reload when I selected it. It looks like everything in between was in a true "paused" state from some brief testing of a few others (that surprised me... I expected fewer). So now I'm going to open up Infinity Blade 2 and play for a minute. That first app I mentioned, which was more recently opened than before as a result of this little test and now at number 5 in the list, had to reload from scratch. Same thing for a handful of others that I just tried in the 10 most recent, though a couple were still properly paused. So as a result of iOS needing more RAM to accommodate the resource-hungry game, it closed a large number of apps that were in a paused state.
That all said, what you are saying isn't wrong, nor is what I said or linked to. There's a lot of "context" not being considered. If you habitually close a running app from the tray that you are just going to re-open in the very near future, then you are certainly hurting yourself. If you have an app that is actively running in the background and you are no longer using but isn't "obvious" it's still active, or worse, poorly coded, then you are unnecessarily wasting your battery and using up RAM. I also think it's fair to say that if, in your list of most recent apps, you have one in a paused state but have no intentions of actually using again in the near future, then closing it would be of benefit. In the case of what I just did, if I have no intention of playing Infinity Blade again today, then closing it wouldn't be a bad idea. Closing it just to re-open it in a couple hours WOULD be a bad idea.
Here's a couple more articles worth reading.
Misconceptions About iOS Multitasking
How iOS Multitasking Really Works