It goes with talk of needing to condition the battery essentially, to teach it to squeeze as much juice out of one power cycle as possible. I've had my phone a little over a month and will let it die before charging whenever it's feasible. With older phones and even my first ipod, I would just charge it whenever (sometimes the battery would be at 5%, 30%, 60%, whatever) and after a while, I noticed that when I would let it go to the point of dieing, it didn't last even close to as long as it originally did. So I will continue to let it drain all the way down when I can, despite no widespread agreement or evidence that it's necessary. Kind of a "to each his own" thing.