Mine live out, TB and shetties, only tend to bring in for a night if it has rained hard for a few days and fields are getting to the mud bath stage to give them a little rest and feet a chance to dry off a bit.
I had them out one winter and they never looked better. I would do it now except there aren't many yards which allow it (or if they do they aren't places i would leave my horse)
My three live out 24/7 all year. They have access to 2 shelters / stables at all times, lots of hay, good feed and rugged as necessary. This includes a woosy TB x who is soon to be clipped. Clipped horses can live out very happily eventhough some people seem to think this is barbaric - lol.