Every time you develop a computer program or app, you should basically be building an API.
Getting in the habit of this will vastly improve modularity of your code, which in turn makes maintenance and future additions greatly simplified.
And, imagine, if you ever want to reuse code from one project in another project, then with proper abstractions you will be able to just quickly import the file(s) and carry on without worry, theoretically. ;)
~ Danial Goodwin ~