If you don’t know what you’ll be working on next week and/or don’t know yet how long next week’s tasks might take, I agree that it might not make sense to plan that far out.

In my case I often have tasks that I know about several weeks (or more) in advance (e.g., giving a talk at a workshop in a few months, submitting recommendation letters that are due in a few weeks). I know how long many of these tasks take. So it makes sense for me to plan it out in advance so I don’t run out of time close to the deadlines.