My stepdad actually taught me this.
When he was in college he had a teacher who basically was a dick and the tests were very hard and whenever you asked the teacher to go over notes again or ask for help he would literally say "no it's your fault you didn't go as fast as I did with the notes."
What a dick.
Anyway for the first two tests he failed them because the teacher went to fast with the notes and the teacher refused to help people.
The last test of the year he got all of his friends notes, I think it was like 7-9 friends, and he studied all of their notes including his. He got an A on the test.
What combining notes does is gives you a chance to study something you might've missed, and the things that everyone wrote down you are more likely to remember.
