Well, some of us have personal reasons for renting points, ie., family illness, new babies, job losses; you name it.
The points you buy begin with what is called a use year. For ex., an August use year allows you to use the number of points you buy between August 1st of any year and ending July 31st of the following year. You also have the option of borrowing the same number of points forward or banking until the following year so that you can either take more vacations, use larger accommodations, longer vacations; the combinations are just about endless.
Say you bought 200 points beginning with an August use year. You have 200 points to use until July 31st 2003. Or, you can bank those points until your next use year, August of 2003-2004 so that you would have 400 points in that time frame. Or you can bank points, use those current points, and borrow forward from your August 2004-2005 use year so that you would then have 600 points available to use within the frame of your August 2003-2004 use year. You can only bank/borrow points within the scope of one year. If you bank points and then don't use them in the next use year, they are invalid.