Sorry, dudes, but billd hit the nail on the head - it is a matter of whether the app does anything or not - and whether you want it to or not.
I, for one, start ATM, kill the apps I want to kill, and then kill ATM - no point in leaving it running if I want responsiveness and to conserve battery power, now it there?
There may not be a need in terms of the usual reasons for using one on Windows - to free memory - but there is most definitely a need for a device that barely gives you 7 hours of use when actively using the device. Any little thing helps.
If this were not the case, then SSDs would not have been designed for laptop use, and OSs would not be trying to get better and better at app and memory management in the first place - we'd all say "To hell with it, I'll just add more memory" and be one with it.