Android 2.1 (at least on the Evo) randomly starts various application, even when not requested by the user. By default, Android does an OK job of killing tasks, but it uses a fairly conservative approach. Apps are aloud to run longer that you might need just in case you need them again. At one point, I had 39 apps running, must of which I did not start. And those were just apps. There are a lot us services that run in the background as well. From time to time (especially if you have recently opened a lot of applications), Android can slow down considerably. This is due to the fact that it's task-killing rate is conservative.
I use Advanced Task Killer because you can set use it's widget to manually kill all tasks, or you can set intervals for killing tasks. You can also kill tasks when the screen is turned off. It even has its own "auto-kill level" which allows the app to more aggressively kill background tasks. Finally, you can exclude certain task that you want to leave alone. There are even more advanced task management apps that allow you to kill services too, but that can be a bit trickier.
The point is that Android CAN manage tasks by itself, but it may not get the job done for some of us. Luckily, we have a lot of options.
I use Advanced Task Killer because you can set use it's widget to manually kill all tasks, or you can set intervals for killing tasks. You can also kill tasks when the screen is turned off. It even has its own "auto-kill level" which allows the app to more aggressively kill background tasks. Finally, you can exclude certain task that you want to leave alone. There are even more advanced task management apps that allow you to kill services too, but that can be a bit trickier.
The point is that Android CAN manage tasks by itself, but it may not get the job done for some of us. Luckily, we have a lot of options.
