I'm probably in the minority, but I disagree with 8. The few times I tried to use supplements I did poorly; when I didn't, I did well. Every professor covers different material, with different points of emphasis. When you use a supplement, you may learn a lot of the material, but there will be parts of the professor's class you won't learn, and there will be parts of the supplement you'll learn that are not relevant to the class.
I also feel like supplements seem to short you on case facts. These can be very important come exam time.
I think supplements are OK if you're going for a B or B+ as opposed to an A, and I also think they're helpful if you genuinely don't understand an issue (though hornbooks are probably better). But overall, I found them to have negative value--they don't teach you much you couldn't learn from reading the case, they take up valuable time, and they can be misleading as to what matters for the exam.