As long as I am fairly happy, I optimize for impacting the world in a positive way. This is because I think this a good proxy for long term deep-rooted happiness. I have found in myself and in others that optimizing for happiness is hard to do without focusing excessively on short-term happiness which leads to hedonic treadmill effects or even in some cases addiction.
Given that you are fairly happy already, optimizing productiveness will allow you have a greater positive impact on the world. I think this is why other commenters have mentioned that optimizing productivity can be a proxy for optimizing long term happiness.
Got it. I was responding specifically to "Why not just do things you enjoy, at a pace that you enjoy?"
I think a really good answer to that is in order to help other people as much as possible. Working on things that are hard or unpleasant or even don't necessarily line up with a specific long term goal in a way you can anticipate will often lead to happiness if it impacts other people positively.
Given that you are fairly happy already, optimizing productiveness will allow you have a greater positive impact on the world. I think this is why other commenters have mentioned that optimizing productivity can be a proxy for optimizing long term happiness.