The lesson emphasizes the importance of using structured data to manage and extend code functionality in Go. By employing a `counts` struct, developers can effectively track multiple properties, such as the total number of words, lines, and bytes from input files. The discussion also highlights the value of converting functions to methods attached to this struct, enhancing code maintainability and minimizing duplication. Furthermore, the lesson illustrates how to implement robust testing for these methods, ensuring correctness by capturing output into buffers instead of relying on standard output. Additionally, it touches on improving user interface design by potentially simplifying function parameters. Overall, this approach streamlines the workflow for handling file counts and testing processes while laying the groundwork for future enhancements through more organized and scalable code design.