So why do this? The main reason is that every time you write, you improve your writing skills. Because writing is a major form of communication, it's one of those topics that's stressed in every subject you study. Most students are expected to write in language arts classes, social studies, science, foreign language, and possibly even math, art, and music.
When you get back to school in the fall and the teacher says, "Write a paper telling me what you did during the summer," you'll be prepared. In fact, your paper will almost write itself because you've already done all the hard work.