Many horse owners, who live in areas where the weather gets to below freezing during the winter, choose to blanket their horse(s) for the winter. Personally, I don't like blanketing my ponies.
Wild horses don't where blankets. For horses, it is more natural for them to grow in a winter coat. I know that some breeds are more accustomed to growing a winter coat than others. A friend of mine owns an arabian horse, who she almost has to blanket during the winter. Since we live in Canada, the winters are harsh, which is far from natural for an arabian horse. Flecky, my Norwegian Fjord Horse, is well into his twenties and I can say he will never need to be blanketed. His coat naturally comes in very thick during the winter.
Money can be tight at many times of the year when you have more than one horse. Blankets are items that many horse owners often have multiple of. Truly, if your horse doesn't need it, why have so many?
I don't know what all you guys out there think, but I prefer not to blanket.