There's a lot more to JROTC than just a class. Not only can you be put in leadership positions within the unit, but being in JROTC can affect the rest of your life, as well.
Like, say for instance you're thinking of joining the military after high school. A person with JROTC experience is more likely to get an ROTC scholarship or acadamy appointment than an equally qualified individual who isn't in JROTC. Also, if you plan on enlisting, you can enter at a higher pay grade; that is, instead of entering as an E-1, with two years, you could go in as an E-2, and in the Army, Navy, Air Force, and National Guard, with three years you could enlist as an E-3. That means more money than someone who goes in as an E-1.
Even if you're not planning on the military, JROTC is still useful. You gain experience in leadership, responsibility, and work skills. These skills help in college, work, and even on extra-curricular activities.