Using functions to promote modular programming serves a few key purposes:
Yields more concise code* by eliminating the need to write out code for the same task multiple times
Improves improve code readability
Helps us more effectively test and debug code
Because we are creating reusable pieces or building blocks of code, we can more readily pinpoint where things are going wrong or not working in our code.
Promotes code reuse and modularity by allowing us to define and call functions for common tasks
This may seem overly-complicated for a relatively simple program.
But imagine all kinds of more complex tasks we might want to accomplish in a programming environment- analyzing data, generating visualizations, creating textures, building interaction objects, etc. All of that becomes possible through functions- modular building blocks that can be combined to accomplish more complex tasks.