One of the most frequent questions we're getting these days is how to close all apps at once -- basically how to force quit or kill every app from the new multitasking/fast app switcher dock Apple introduced in iOS 4 for iPhone and iPod touch and iOS 4.2 for iPad.
The short answer is you don't need to. Really. If you've been worried about it, relax. It's all good.
For the long answer, read on after the break!
Multitasking is more of a marketing terms these days than a technical one. Don't think of your iPhone as a Windows or Mac OS X machine because it's not. It isn't Windows Mobile or even Android either. iOS doesn't work that way. It doesn't (most of the time) leave a bunch of rogue processes running in the background that have to be force-quit.
iOS manages all that for you. Most applications, when you exit them, save their state and "go to sleep". So if you were playing a game or looking at Settings and then hit the home button or switch to another app, it keeps track of where you were in the game or what page you were on in Settings, then stops the app. When you tap the icon to launch the game or Settings again, it reads the state and returns you to the same place in the app. It only seems like it was multitasking -- it wasn't. If you haven't used an app in a long time, iOS might not even keep the saved state (you'll notice the app re-launched and shows you a splash screen instead of going back to the last place you left it.)
This means, for most apps, you never -- not ever -- need to "delete" them or close them from the multitasking dock. You might feel a desire to, even an obsession to. But you really don't need to. Really. (Breath out!)
The only exceptions are:
There will be rare -- rare -- occasions when a specific app, even an Apple app like Mail, stops working properly and a force-quit can get it to restart and behave itself. Once an a while your iPhone or iPad might get really sluggish and closing any big, recently played games might help.
But when it comes to closing ALL apps, ALL the time, just remember:
You don't ever -- never as in not ever -- have to close ALL the apps in your multitasking, fast app switcher dock. It's a sniper rifle, not a nuke. So just relax and enjoy your apps and let iOS do the heavy lifting for you.