Originally Posted by DancingArabian
HOWEVER, if they can walk in and out freely, then it's fine.
Yep, because then it's just a walk-in shed type deal, and the horses have a way of escape should things get ugly.
During normal weather, all 3 of my stalls are open and the horses can go in and out as they please. I'll often find all 3 of them standing together in one stall, or more normally, 2 standing in the stall and one with his head inside but his body outside in the weather.
Very rarely do I stall my horses but when I do, they each have their own. My stalls are 10' X 24', so nice and big.