Internships provide real world experience - a key factor employers look for when hiring.  Internships encourage you to apply your class knowledge to solve problems and contribute to an organization, develop transferable skills that you can use to compete for entry-level jobs, and expand your professional network.  There is no substitute for experience, so the more experience you seek out through informational interviews, job shadowing, and internships, the more prepared you will be to compete for the jobs you want after graduation.