Keep in mind that use year is basically of no importance except in the instances where you need to cancel a reservation at short notice.
The amount of points you can bank diminishes as you get closer to the end of your use year. So if you ever did have to cancel a reservation, you would want that ressie to be near the beginning of your use year rather than the end of it. In your case let's assume October vacations with an August use year, and with a November use year.
You make a ressie for October 2003 using your August 2003 points. You cancel in September but still more than 30 days before your planned trip (under 30 days is a special case and imposses additional restrictions)
Since your August use year points are good through July of 2004, you have plenty of time to book another trip, or bank the points.
Now on the other hand, if your UY was November then you're using November 2002 points for your October 2003 vacation. (Nov 2002 goes from Nov 1, 2002 thru Oct 31, 2003.
You cancel your ressie in September 2003. However you are now past any banking deadlines for November use years. You would have to use those points by Oct 31, 2003 or lose them.
So bottom line is you basically want a use year that begins a few months before your normal planned vacation dates.
Again, this only comes into play when you cancel reservations. If you never cancel reservations, then use year becomes nothing more than the anniversary date of when you receive new points every year.