The importance of use year is minimal. The only time it really becomes any issue at all is if you have to cancel a ressie last minute. So if you usually travel the same time every year, it might be important to have a use year that is just before the time you usually travel so there is plenty of flexibility with rebanking. That being said, we have been members for nearly 10 years, and we have never had to cancel a ressie last minute.
Use year is the month your points are added to your account, and banking deadlines are based on that month. That means that you are unable to bank in the last 2 months of your use year, so a cancelation might mean the loss of points. Remember that use year has nothing to do with when you can make a reservation....only when you can bank and when you get new points.