Android inactive tasks, this is how it works
I read a lot of people saying that because Android is based on Linux (the kernel at least) it handles multi tasking much better than Windows and that is why you don't need a task killer.
This is actually not the reason. Android will run programs in the background, but when it runs out of resources it will close running applications automatically (that's something linux and windows do not). This can lead to issues as when you come back to a closed application, the user will expect the application to be in the state in which he or she left it. To overcome this, Android applications store their state. When they are started again, the state is loaded and it appears the application was running all the time.
The only reason to close applications is to limit CPU usage. Applications can respond to all kinds of events and if you don't need them, you can close them. This may make a bit of a difference.