The Productivity Cycle by Alex Sexton is a wonderful article that has stuck with me over the years. There is a bunch of it that is about caffeine consumption. Alex cites actual research and provides context, so definitely read the article, but the gist of it is this:

Consuming caffeine in time for it to affect you at the exact peak of your “focus wave” effectively makes the highs higher, and the lows lower. The rich get richer, while the poor get poorer. It’s like the sad state of our socioeconomic classes, except not awful, and for brain power!

Rather than using caffeine to fight off being tired, just be tired. But when you’re bouncing back and going into a high-energy period, that’s when you caffeinate, to make a productive period even more powerful. 

I thought of this as I was considering how I pair energy and tasks. If I’m working on something extraordinarily hard, I’ll consider caffeinating a high. If I need more average hours to knock out a lot of stuff that just takes time, I’d consider caffeinating a low.