You would only do it if you are at your 7 or 11 month window and are booking at a particularly busy time. Here's an example:
Let's say you wanted to stay in one of the GV at OKW during XMAS (12/21-28). Assuming you own at OKW, you could book 11 months from the check-out date. You could wait (and take your chances) until 1/28 and make the call for the whole week, or you begin by calling 1/21 and make the reserveration for 12/21, then on 1/22 you make it for 12/22, and so on...
I hope this helps...