When you buy a DVC membership, you're actually purchasing a real estate interest in a particular resort. This is called your 'home resort'. You may make reservations at your home resort starting at 11 months out from the start date of your stay.
You can make reservations at all other DVC resorts beginning 7 months out from the start date of your stay.
Since at 7 months, you're competing with the rest of the membership for the remaining resort rooms, there can be some risk in getting a reservation, especially at certain times of year and certain resorts.
So, let's say you really want to stay at BCV during Food and Wine festival, but you own at AKV. You know that it can be really tough to get BCV reservations for October at 7 months, so to be sure that you have something reserved on property for your October stay, you make your reservation at your home resort, AKV, at 11 months out. When the 7 month window opens, you then attempt to switch your reservations to BCV.