•I only blanket my horses when temperatures reach below a certain degree (i.e., 5 or 10F): 31.23% (653)
•No, my horse is very hairy and doesn't need a blanket: 30.89% (646)
•Yes, but I don't keep my horse clipped: 21.95% (459)
•Yes, because my horse stays outside all the time: 8.27% (173)
•Yes, I keep my horse clipped: 7.65% (160)
It appears that at one time or another, the majority of horse owners do blanket their horses. The reasons why, though, vary as much as any other opinion in the horse world.
I don't think really any of these opinions are wrong, either. I think blanketing is something that is only neccessary in extreme cases (rescued horses who have no body fat or no adequate coat because of rain rot, for example), and I think it depends upon the horse as much as it does the owner. Horses, like people, vary greatly in how much extreme weather impacts them.
Eddie, my stallion whom I lost in June, loved the cold weather. He absolutely thrived in it. When the temps dipped below freezing, he could always be found stirring up trouble and playing with his jolly ball. I got the best video of him in cold weather because that's when he'd really enjoy himself. It was obvious, too, that he despised blankets. He loved being cool and never seemed too cold at all. Plus, the blanket restricted his movement a little since, due to his injury, he was not able to move like a normal horse. He obviously preferred to be without a blanket, and so I never blanketed him. Summers were brutal for him, though, which I (and our wonderful friend Vicki) would try to remedy with a daily hosing down (which he'd come up and stand for, unhaltered).
Eddie didn't pass along this trait to all of his foals. Paula will actually pace for her blanket when the temps drop (her pacing is her sign for "I want something" and I can usually tell right off the bat what it is by the situation--she always stops as soon as I give her what she wants, silly girl). Fabian gets upset if he's not the first one in the pen that I blanket. He shows his displeasure by pulling his blanket off the railing and pawing it into the dirt. Both will lower their heads and duck down into the neck hole of the blanket, "helping" me put it on them in their own way. Neither one of them appreciates the cold weather at all. Paula will poke her head through the window of her shelter and try to get me to feed her inside of it. She'd love to be stalled during this sort of weather, but unfortunately I just don't have those kind of facilites yet.
Bambi and Moose really don't care either way. I probably don't have to blanket Moose as his coat is very thick, but he's growing and to me, whatever calories he doesn't use for keeping warm can only help with his growth. Bambi has a fairly thin coat, and she's a little more delicate than the others. She's a little high maintenance, so the more I can do to help her be healthy and comfortable, I'll do it. She stands readily for the blanket, and doesn't seem to mind either way.
Another reason I blanket Moose is it gives me one more excuse to work with him. He's a young colt (gelding) and while he's halter broke, broke to tie, has been clipped, trimmed, lunged, loaded, etc., he's far from a been-there-done-that gelding (of course). The more I can ask different things of him, the better off he'll be in his training. This is also the reason why I blanket Betty when the weather gets bad. I don't blanket her as often as the others because her coat is very, very thick and she is in good body condition. I think its worse for a horse to be too hot than too cold, so I typically err on the side of cold. But when the temperature drops, I halter her, ask her to give, then slide the blanket over her head and ask her to "whoa" while I fasten the buckles. She usually does very well, but she's technically not even halter broke, so the more I can do with her like this, the closer we get to catching her up on her training. She's starting to come up to me on her own and doesn't shy from my sudden movements anymore, so even with limited handling, the approach of just doing little everyday things with her (like blanketing) has improved her level of training.
So, that's why you'll sometimes see my horses pictures with blankets and sometimes without. I basically let them tell me, in their own way, if they'd like one, then I gauge other aspects like how bad the weather is, their condition, and if I can use blanketing as a training tool I will. I agree that most horses don't really need blankets, but for my own kids, at this moment in time, it works pretty well for us to blanket during extreme weather, even if it is for a wide range of reasons.