Most horses do not need a blanket, and if your horse doesn't need one don't give him one unless it's very, very cold out, probably in the teens or less. The only reason some horses wear them, is because some breeds like TBs and Arabs are desert breeds. They don't grow as good a coat. However, I know one TB that needs a coat during the thirties, because he grows hardly any coat at all, and another TB that doesn't need a blanket at all unless it's very cold out. See how your horse's coat grows, and decide with a knowledgable horse-person whether he will need a blanket or not.
A horse technically does not need a blanket. Those who show year around use blankets to prevent the horse from putting on a heavy winter coat for looks only really. Some horses who are sick or cannot produce a winter coat will need blankets. In the wild the weak ones would die out and the strong ones would live...
Some breeds grow very good winter coats and others don't I have a quater horse who looks like a bear in the winter and a standardbred that only gets a light winter coat so one wears one and the other one dosent! Unless it gets in the teens or lower then they both do
Someone's care more about their horse than others do.