Should your instructors require attendance at class?

If your instructor says attendance is mandatory, maybe that forces you to go and you learn more and get better grades. Or maybe you go but zone out or surf the Web, learning little or nothing. I don't require attendance, but almost all of my students come anyway. Why? Because they know the quizzes and tests are likely to focus on topics I've discussed in class. What do you think? Does requiring attendance help you or not?