No reasons, but for me an explanation. I have blanketed and not blanketed - depends on the horse and what he is being used for. I religiously blanketed one horse every night all winter because he lost so much weight using his body fat for heat even though he had hay 24/7 and grain too. I got tired of "feeding the winter" so I blanketed him and it stopped the problem. If I have horses that I use heavily I will blanket because I trace clip. Again, I think it is the horse, it's age and how well it deals with the elements that should make the decision to blanket or not. Left to their own devices horses will develop a heavy enough coat to be comfortable in the winter. If you start blanketing in the beginning of the winter though you have to continue as it is not fair to the horse to do otherwise.
Lee
Everything will be okay in the end. If it's not okay, then it's not the end !