It makes complete sense, but I've only recently discovered the importance of side projects, so I thought I would share some thoughts about it for fellow students.
When you go looking for a co-op or internship or a job, you may be asked for things you've worked on. Although school projects demonstrate how well you can preform at assignments, some companies are equally interested in what how well you can preform at things you are interested in. Working on your own projects is great study, and a great time to practice and hone your skills. If your interests are making add-ons for firefox, or reading your dog's brain waves, give it a shot, it can't hurt.
I was lucky, and had a genuine interest in side projects, and if you want to do well in the computer science world, or any field really, you must develop a genuine interest in your field. In your eyes, they can become really fun projects that show your skills. In your employer's eyes they are a clear representation of your interests and how you can be effectively utilized within a company.