I actually spoke with a dean of admissions and asked him about the waitlist. He said that some years they have taken zero people off the waitlist and other years they have taken off as many as 40. Then he told me about a new policy that LSAC has instituted in which they tell schools the names of applicants who have double deposited.
He said that in their acceptance package it says that people who put down multiple deposits will have their acceptance reneged. And it makes perfect sense why this is the case.
The whole purpose is to ensure that both students and schools can make decisions quicker. It forces the student who has been ADMITTED (waitlist doesn't matter, you don't need to put a deposit down yet), to decide quicker, which enables schools to make a more exact waitlist. It will also help schools notify waitlisted people sooner because they will have more exact numbers about who will be attending based on deposits. It has nothing to do with what is ethical or not, it has to do with what is more efficient.
The new program will make students and schools make decisions quicker. It will benefit all.