The numbers have always been there.
I think they help when a flight is cancelled our something so they can start accomidating people. I've seen them do this and they do it by those numbers. For example if you have number 1 on yours, you were the first person to check in so you'll get accomidated first. They don't always do that however. But I have seen them do it before.
I hope that helps
P.S. They may also use those numbers for the future if they change their boarding procedures, we just have to wait and see.