The best way to get hay to your farm animals is with the large round bales of hay, but you can't just set the bale out in the middle of the field, you have to unroll it. Three point bale unrollers grasp the hay bale in the center of both sides, and turn on a central axle allowing the friction from the ground to "grab" the hay and start unrolling the bale to make it easier to spread out. If you have ever tried to scatter out a round bale of hay by hand, you know how long it can take to separate all of the hay into a usable area, with the bale unroller, it simply connects to the back of your tractor and rolls out like a carpet no pitchfork required.
Many people have tried using other unsafe ways to unroll massive hay bales, but the danger and risk that is present with such actions is not worth it. Rolling one of these huge rolls down a large hill, or off of the front loader of a tractor can injure someone in the way, or even damage a fence if it is rolled too close to one. The low price and availability of these attachments really makes sense to do things the right way and spread the hay out with your tractor. The best part about 3 point bale unrollers is that they come in various sizes to fit any bale thickness you find.
Some people have even used these attachments in a different kind of way, simply unrolling large round bales, then going over the hay with a square baler easily increasing the price of the hay, and making a few quick bucks, this allows for ultimate control of how fast and where your round bale gets unrolled at, keeping it where you need it and avoiding disasters with people, animals, sheds, fences, or other common farmland obstacles.
Leinbach is one of the oldest manufacturers of 3 point bale unrollers, they have been making tractor attachments since 1971, and they also have a full line of other popular 3 point and farming attachments. Other manufacturers are Southern farm, and a rumored Everyting Attachments bale unroller is seemingly in production. A side note about Everything Attachments is that they have been in business as a tractor/attachment dealer since 1941, and has always been a very knowledgeable family-run business bringing decades of end user experience to attachment sales and now manufacturing with their own brand of tractor 3 point attachments.