Believe it or not, writing tests can help you structure your application properly which eventually leads to better code. Some developers even advise others developers to write tests before the main program, as it helps you envision how your functions/methods are going to look and work before you start writing the main program.
Let's think of our web application as a hotel, you have customers that stay in the hotel and order food from the hotel's restaurant. Let's also assume that we have only 3 cooks and numerous "room service staff"
Basically, a flask blueprint is a way for you to organize your flask application into smaller and re-usable applications Just like a normal flask application, a blueprint defines a collection of views, templates and static assets.