Of course the absolute easiest way of doing it is
WHERE YEAR([date]) = 2015
But that's not sargable. It doesn't matter if you're looking at only a few thousand rows in your table. But if your table has hundreds of thousands or millions of rows, then performance will suffer greatly.
I would argue that it does matter. There is an adage that "If you fail to plan, you plan to fail." This is very applicable to this situation, because using the SARGable method plans for growth, whereas the non-SARGable method does not.
Drew
I should have been more precise in my wording.
"If you have a lower number of records, and you KNOW the number of records will not be increasing significantly, then you can use a non-Sargable function."