Planning a day or a week in advance works because it pays the brain's decision cost once rather than dozens of times.

Professor of Neurology at the University of Oxford

Every decision has a cost in terms as we've seen the brain having to put in invest fuel to make that decision. So if you're having to do that every time you make a decision, that can seem very burdensome. Whereas if you did it once in a big way where you planned it out for the day or the week, maybe the costs in terms of the activation energy required for the brain is much lower for you if you do that.