Use year determines your banking deadlines. It has nothing to do with when you may call to make a reservation.
Banking deadlines can be important if you have to cancel a vacation that occurs late in your use year.
For example, let's say you have a February use year and usually travel in March opr April.
Your 2007 use year points are good for vacation between 2/1/2007 and 1/31/2008.
Your 2008 use year points are good for vacation between 2/1/2008 and 1/31/2009.
Your 2009 use year points are good for vacation between 2/1/2009 and 1/31/2010.
etc.
You may bank up to 100% of your annual allotment of points as long as you call to do it before the end of the 6th month following the start of your use year. So with a February use year, the 100% deadline is the following July 31st. You may bank up to 50% if you do it before the end of the ninth month and up to 25% if you do it before the end of the 10th month. No banking is allowed durign the last two months of your use year.
Let say you have to cancel an April 2007 trip, using your 2007 use year points. As long as you cancel at least 31 days prior to the scheduled arrival, your points will be returned to your account. You have until the following January 31 to use them (or lose them) or you may bank them into your 2008 use year.
But if you had a June use year and had to cancel the same trip, you would only have until May 31, 2007 to use the points (or lose them). You cannot bank at all during April and May with a June use year, and assuming you cancelled at least 31 days in advance, you could only bank up to 25% of your total annual allotment if you called before the end of March to do it.
With a June use year, you would have used 2006 use year points to book the April 2007 vacation because April of 2007 falls within the June 2006 use year.
With a June use year -
Your 2006 use year points are good for vacation between 6/1/2006 and 5/31/2007.
Your 2007 use year points are good for vacation between 6/1/2007 and 5/31/2008.
Your 2008 use year points are good for vacation between 6/1/2008 and 5/31/2009.
etc.
With any use year, the first day you can call for an April 2007 vacation at your home resort was 11 months prior to check out - May, 2006.