It is a concept when you’re doing not fun things first, slowly increasing level of entertaining through the day.
It’s hard to start doing boring things after completing a more entertaining one. Plus it’s connected with energy - boring things require much more of it, and generally you have more energy in the morning.
So the consequence is: you might want to hangout, do sports, play video games in the evening. And then, it’s good to decrease entertainment levels closer to sleep time, to fall asleep more easily.