Rhetoric 105 is all about writing. But writing requires research, critical thinking, and analysis of the subject. The class teaches you these three things through writing and it stays with you for life. I can see why a rhetoric class is required for all freshman. Throughout your college career, writing becomes an essential part of your toolkit because you are needed to explain yourself to your audience many times.
Learning how to write prepares you for lab reports, presentations, essays, and even analysis. To write about a topic, you must know about the topic, to know about the topic, you must do sufficient research on the topic. Essentially, writing teaches you how to learn and analyze a topic.