To expand on this a bit, look at location services on a phone. A "fine" location access event is a "high power" event, it takes a lot of battery and should be

To expand on this a bit, look at location services on a phone. A "fine" location access event is a "high power" event, it takes a lot of battery and should be done as infrequently as possible. Apps on android have the ability to say "i want to get location at least once every 30 minutes". A naive implementation would give every app that asks for this a timer, and when that timer ticks off, that app gets location information. For 5 apps, that could mean 5 times every 30 minutes! But android is a bit "smarter", it will do it once in the 30 minute period, then give that same info to all 5 apps. But then the question is, who caused that battery usage? None of them? All of them? Should adding a 6th app into the mix cause all of the battery usage of the other 5 to go down proportionally? Technically that 6th app is pretty much "free" in terms of actual power usage... What about if an app says "I want location whenever you get it, but I never want to trigger it on my own", where do you allocate it's usage? And that's just one API. Now imagine that with wakelocks, radio usage, accelerometer/gyroscope usage, etc...