Depended on the class for me. Most professors didn't take attendance. We were generally allowed about 3 absences. I probably missed a total of 6 classes during the three years I was in law school. For classes like Tax, missing anything could be a total disaster. For my criminal procedure class, you could miss a few days and it wouldn't matter much, because the professor just went over the materials we were assigned without adding much.
If you really need to miss class, it sometimes helps to speak to the professor and ask if there is anything you should be focusing on in the reading for the days you are missing. Also, getting notes from 2 different classmates is crucial to see what was emphasized in class.
Missing class here and there is no biggie. Making it a habit is a bad idea.