Well from what i learned, your phone has running apps in the foreground, background, hidden, etc. Now if u kill the apps that the phone needs to run on then your phone will probably not work rt. For instance sync settings, file readers. Stuff like that. I used to have advanced app killer, and i found it to be annoying. I would kill apps that i never opened then i noticed apps reopening. Plus i never reallized it but my battery was dieing faster. I got rid of it and was able to listen to 4hrs of pandora and my battery used up a fraction then when it had the app killer. I recently got auto memory manager. And i found it to be a lot useful. Plus it kinda acts like an app killer cuz it has auto kill. U can set how much memory to use, and see a list of running apps. I know the phone has a running list on it, but amm does it better. U see evrythn and it tells u what each app is and the importance to ur phone. Check it out auto memory manager. Like i said i just got it so i'm still not a 100% about it, but it seems to work well.