As a rule of thumb, absenteeism is directly proportional to poor academic performance especially when attendance is sometimes scored by some lecturers.

Also, students may miss out on very relevant information when doing some examinations or investigations which they may hardly see in any book. The cost of this can sometimes be priceless for instance in the case of a practical final exam assessment.

I imagine it depends on the type of class, fully theoretical classes can be recovered with further study at home, but more practical classes are irreplaceable