anyone wanna go into a bit more detail? i'm also curious about this too. i've been using ATK. by the looks of it there are a lot of apps running in the background of my phone that i don't want, why shouldn't i be using ATK? just wondering
As android is running linux based variant by default it shares few similarities. As one of them includes superior memory management which is not same as WinMo. In our world UNIX world (long before this POS Android newbie stuff was even born) we have a saying that unused memory is wasted memory. So when anything is allocated it is cached and its not released until anything requires it to be reallocated. Now this can happen from few things as memory is still cached if user were to access it by rerunning it then it will still be available but if the resource is unused based on the access recalls its relased based on chronologically.
Now anyone who thinks task management is not required even on UNIX/Linux much less on Android is simply a fool who shouldn't do anything as they are harm to the system. With that being said if you are required to shut something down forcefully due to memory leak or other factors you should do it only if you know what you are doing as it will not be fully released until you do warm boot.
If you need greater access to system resource then I suggest you take control of service and disable things that you do not need. Once again if you don't know what you are doing then leave it alone. As you can disable service at boot and some service do restart in that case you can also setup policies to shut it down if its restarted.
^ now tell me I don't know about memory efficiency.
Task killers can cause increased resource drain by stopping services needed for background functions of the device. Those services will attempt to restart, be stopped by the TK, start again, etc ad infinitum.
They also can cause sync loops in apps which are configured to autosync, such as Facebook, Weather, Gmail, etc, for similar reasons that the services are affected as described above, only worse, because as more than one syncing app attempts to grab data, they can overlap because the TK has interrupted the natural cycle, causing the app or widget to try to sync at an instant when another one (or two) is.
They were not even needed in early Android OSs because there is a simple menu path to each app/widget which can be used by a responsible device owner to kill services, clear cache and data if needed, etc.
Task killers are a bit like a trusted burglar alarm installer who has too much information about your valuables and how to get to them.
uninstalling ATK as i'm typing this. 
