So, that media player I opened and quit using 8 hours ago and is still shown as running, is basically just sitting there, barely using any power and memory?
Once Android starts to run low on power/memory, it will shut the program down as needed?
Bingo.
Its saving the app in a "hibernation" state that takes up a teeny tiny smidge of memory and no CPU.
The second you pull the media app up, it "wakes up" the app and starts feeding it CPU power.
Unless your media player is actively playing video/pic/music, it is drawing no CPU once it is "hibernated" by the OS. It does however take up a tiny bit of memory.
The reason task-killers suck is because if you KILL an app, it wipes the memory clean. So when you open that app later, it has to do a lot more work(thus eat more battery) to retreive the data from ROM or SD card rather than active memory.
People complained about Windows for the same reasons and they're just as wrong. Windows Vista / 7's memory management utilizes as much memory as it can so that apps load faster! If you use say, photoshop, a lot, Vista/7 will pre-load all of that data from disk to ram. So when you launch photoshop, it will launch fast because its already in memory!
For some reason people think that using up memory is bad and that having gigs of free memory is good.
No. On a modern OS, be it Android, WebOS, OSX or Vista/7, free memory is wasted memory.
My personal desktop has 6gb of memory. When i boot the machine, i have 1-2 gb free. The other 4gb is being used to preload apps. Now, if i open a file that requires say, 5 gb of memory, windows UNLOADS the idle programs!
Repeat after me, free memory is wasted memory.
Ram is faster than movinand flash which is faster than microsd
So, it always pays to have as much as possible preloaded into memory.