Your Use Year is the start point every year when you get your allotment of points. From that date, you get your "banking" windows. For example, if you have a February Use Year, every February 1 you get your points to use from February-January 31 of the next year. By the end of July, you can bank 100% of your points. October 31 is the cutoff for banking 50% of your points and November 30 is your last opportunity to bank any points. You can bank up to 25% at that point.
If you are taking a vacation late in your Use Year (say December-January for the February Use Year example) and you cancel close to the date, your ability to bank your points is limited. For example again, if you have 200 points, during November you could only bank 50 points and in December-January you can't bank any points. Let's say you have a vacation planned for mid-December using 150 points. In November, you have to cancel. If you do so 31 days before the start of your vacation all your points are returned to you to use. But, you must use them by January 31. You will only be able to bank 50 of them. You have 100 points that must be used.
So, Use Year plays a part when you are cancelling a trip late in your Use Year. Unless you vacation the same time every year and are prone to cancel late in your Use Year, it's not much of a concern.