You are absolutely right. There is no reason to have one use year month over another. It has nothing to do with making reservations at all, nothing.
The only concern for use year is canceling. If you have a June use year and you usually vacation in May, and aunt Sally comes down with the gout and you have to cancel you vacation to be with her....those points need to be used by the end of May, Aunt Sally's gout may not have popped up early enough for you to bank any points at all.
Now, if you have an April use year and Aunt sally needs you, as long as she lets you know more then 30 days before your trip, cancelling that trip still leaves you with all year to bank or use your points.
The ONLY consideration for use year has to do with cancelations. In general, a use year slightly before your usual vacation period is best....but it has never really been a factor in my 9 years of membership.
"From each according to his ability, to each according to his needs", Karl Marx, pretty sick, huh?