well the evo 3d comes with a stock task killer thats always running.. its not a app from market rather than one that comes with the phone so how do i disable it , is it wise.
Although Android 2.2 and above do manage memory a lot better than previous versions, occasionally, one might want to kill a misbehaving app. In those instances, you can use the built-in task manager to kill the specific app.
In Sense 3.0 devices, just drag down the notification bar and choose Quick Settings, then click on Total Memory. That will bring up the Task Manager. Hit the "X" on anything you want to kill.
The problem with automated task killers like "Advanced Task Killer" is that people don't know how to use them properly. They turn on the automated features and the program starts killing apps and services indiscriminately. This causes Android to reload those apps/services (because they really should be loaded for optimal performance), which in turn burns more battery (uses CPU cycles). Then people complain that their battery life is poor.
People don't understand how Android manages memory. The OS pre-loads programs that are used often so they are available instantly. That doesn't mean that they are actually running. They are just sitting idle in memory.
It also maintains a list of previously-run apps (the 8 most recent). Being on that list, however, doesn't mean that the app is actually running. Its icon is there for you to recall an app that you recently used (whether it is actively running, has been killed, or is sitting idle).
With all that said, you can disable the built-in Sense 3.0 Task Manager by pressing Menu --> Settings --> Applications, then unchecking the "Start Automatically--Auto launch task manager after device startup" checkbox. I don't recommend doing it. I think the EVO 3D runs fine with it.
If you are experiencing lag, then you most likely have a poorly-coded program running. I haven't seen any lag on my EVO 3D, but that's not to say that it couldn't have some under extreme conditions. YMMV.
One more thing: There is a difference between a "Task Killer" and a "Task Manager". The task killer is designed to kill tasks in the background (without user intervention). Advanced Task Killer has that capability (although you can turn it off). A task manager (like what is built into Sense 3.0) doesn't kill a task unless you actually tell it to. Otherwise, it only displays the running apps and how much memory they're using.