Basically nothing. It simply gives you the freedom to decide if you want to set priorities based on days or weeks.
There are people who prefer to see their to-dos on a weekly basis, and those who want to prioritize things even further by setting a MAIN PRIORITY, which is something necessary, but once that’s done, everything starts to progress forward.
The daily activities let you keep your priorities, add some playful elements to your work, and if your MAIN PRIORITY is too hard, you can divide it into smaller tasks. It’s recommended to use the daily planner with the weekly planner as the two planners promote productivity.