I live in one of the coldest winter climates you can get, and want to still have horses :)
I only blanket if a horse seems to individually need it, and then I limit the use as much as possible so that it doesn't become necessary all winter. My horses tend to need blanketing more in November if ever. We have a 19 year old gelding who chooses that time to shed all the way out before growing in his winter coat. My stallion had not yet grown a good winter coat this November, so was miserable and had a blanket on at night for a few weeks.
This time of year, the horses have adjusted and really started to get their nice winter coats (although they will get thicker yet), so I will only blanket if one of them really seems to struggle during a cold snap. I try to increase hay intake though rather than go to the blanket because if you are not very careful about removing blankets, brushing out coats, airing out blankets, etc., blanketing can actually take away some of the insulating ability the horses' coats naturally have.
We have had 30 degree F below zero cold snaps and not needed to blanket our horses. Their barns are also not heated unless there is a health emergency...so they act only as a wind/snow block. We just increase hay & sometimes grain during cold snaps to make up for calories burned to stay warm.
My vote is no blanketing in general, but yes blanket based on individual need.
Also, I do use sheets during show season to keep coats nice and clean.