Because you can make your plan your own. What is important to you? Work, family life or personal time?
You have a lot of options when it comes to planning your daily schedule:
1) Using the standard weekly calendar
2) The monthly calendar (useful for long term plans but not so helpful with short term goals and deadlines). 
3) A combination of all above. But what if I told you that there's an even better option than the combination?
The customizable daily planner!
With the daily planner, you get to choose what works best for YOU. You decide how many days in a week you want to work, how much sleep you need, how much exercise you do, and how much time you spend on other activities like hobbies, socializing, etc.
This way, you'll be able to create a schedule that is tailored to your needs and preferences. And because you're creating it yourself, you'll know exactly what's going into your day, which will help keep you focused and productive.