Let's say you have a mobile app used by 1 billion people every day. It sounds crazy, but I bet a fair number of people in this forum contribute to such an application.
Imagine you want to make an optimization that increases battery life by 1%. Assume a 30Wh battery and that it's charged once per day. Over the two year lifetime of the phone, at $0.10 per KWh, that change would save your users 21.9 million dollars in aggregate. Even with a team of 40 people making $500,000 per year working for a year, you still increase the efficiency of society with that change!
(I know, this ignores the opportunity cost of adding a new feature before your competitor, or focusing on something that will bring more user happiness, or the externality that users don't notice the $0.00003 they're paying to supply your app with electricity. But the point is, we have a lot of power, and our time is much cheaper when multiplied proportionally to that impact.)
