Programming interviews are stressful. They require a set of skills that we don't exercise daily as developers. Solving problems on a whiteboard is not the same as writing a program in our favorite development environment. Speaking in a presentation style is something only done rarely. Beginner algorithms also don't get used very often outside of school.
Mock Interviews are the perfect way to brush up on these underused skills. Get valuable feedback from real engineers that run programming inteiews regularly. Learn what skills you need to practice before you ever step into a real interview. Get useful tips on how to present yourself in a way interviewers will love.