Why you should be on time?

Why you should be to class on time? This is a question asked by every teacher, and there is a different answere from every student. I think you should be on time so that class can start as schedualed and run efficently. If over half of the class isn't there on time the teacher cant start the class. If you are the student that isn't getting to class on time you could be holding the rest of the class behind or you could be missing som important information if the teacher decides to go on with out you.