There are many reasons why planning ahead is beneficial to achieve your goals and to improve your health.
Fill your plan with the most important things for you, will avoid that you lose time with the superficial tasks.
Knowing what you have to do at any given time, allows you not to think about what you have to do now, and directly start doing it.
You will be prepared for what is coming.
After completing a task that was in your plan you will feel rewarded because you finished something that you told yourself you wanted to do.
Because you have time for planning, you can focus on the big picture of what you want to achieve. You don't have to think about the details.
Successful people plan ahead. Not only their weekly agenda but also their years. Just look at the first sentence of Tesla's CEO Master Plans 2.
"The first master plan that I wrote 10 years ago is now in the final stages of completion."
Yes, 10 years.
To be able to accomplish big things in life, it's better to have a plan.
Knowing which steps to make. Knowing what goes first, and what goes second...