> No one ever tweaks that one setting even though they should
That entirely depends on the use-case. Most people running FFMpeg do it as a once off thing - and if those people like me, when I rip a movie I want the highest quality and lowest size I can get, and I'm happy that the default sacrifices speed for quality and size. The processing can be slow because I'm doing it only once. If you're in the business of encoding video and do it all day everyday, your calculus will be different and you won't be using the defaults regardless.
That depends under what conditions the energy is used. In a place where you need extra energy for cooling yes. In my home no. I live in a cold place, so I need heating the bigger part of the year. And I heat using electricity (which might be stupid, but that's the house was built 30 years ago). So whatever energy my computer wastes, I save it in my heating bill. Computer energy is free, except during some warm summer weeks.
That entirely depends on the use-case. Most people running FFMpeg do it as a once off thing - and if those people like me, when I rip a movie I want the highest quality and lowest size I can get, and I'm happy that the default sacrifices speed for quality and size. The processing can be slow because I'm doing it only once. If you're in the business of encoding video and do it all day everyday, your calculus will be different and you won't be using the defaults regardless.