The consequences for missing lectures are different than they are for missing discussion sections. After they miss a lecture, students are required to contact me to explain the reason(s) why. In almost all cases, this will be sufficient to offset the absence. (Again: even if you skipped only because you don’t find the lectures useful; I would like to hear that—perhaps along with some suggestions for improvement!)
Discussion sections are another matter. Attendance is naturally a prerequisite of participation. I believe strongly in the power of discussion as a pedagogical vehicle; and students should know that I think a considerable amount of independent work would be required to compensate for missed discussions. As a result, those who are considering missing a discussion section are encouraged to consult with me about suitable makeup work before they do so. Those who fall victim to debilitating illness must contact me as soon as they are able to arrange suitable substitute work.