This is not to say that this is for people who have trouble saving $1300. I save by having money automatically taken out, I put money in to my retirement savings account, and every time I am in possession of $5 bill, it goes into savings.
This is just an additional, easy, not all that noticeable way of saving money (for me). This would pay for a guilt free all inclusive vacation next winter, or in my case pay for travel/presentation/new dress for my brothers wedding in December.
It could also be additional money that gets put on your mortgage, or car loan. Or stop at the 51st week and there you have Christmas gift money. There are plenty of reasons to do it. And like said above, if you can't manage the last $100 then that's fine. Put what you can.