And if you're doing something that sucks up battery, you should know about it and act accordingly.
If you're not doing heavy lifting, It's just not something you should have to think about as an app developer, there are so many other areas to focus on to keep users happy.
Apple has a few WWDC sessions that talk about it I think.
Here's what they have to say in their "performance tuning" section:
https://developer.apple.com/library/ios/documentation/iphone...