Long story short, the University of MN studied the length of time it would take horses to eat a certain amount of hay either from the ground, in a regular hay net, a medium hay net, or a small hole hay net. There was no difference between feeding on the ground and out of a regular hay net, but the medium and small hole hay net increased their time. Ok, cool, what does this mean for us?
As a boarder, I am constantly trying to do what's best for my horse without being the worst boarder ever and asking the BM/BO to do something they find ridiculous. In case you don't buy your own hay, it's $$$$. Feeding lots of hay makes a boarding barn costs go up quite a bit, especially when you think of all the hay that gets wasted by horses peeing on it, grinding it into their stalls, and otherwise not eating it because it's not up to snuff. It's also possible that with an air fern type (aka NOT Digby) your horse can't eat hay/grass 24/7 because it will become fat (aka me when I eat ALL THE CARBS!!!!) and that isn't good either. But it's SO important for horses to be eating as much forage as possible. So where do we balance the horse being able to "graze" as much as they'd like versus spending all the barns money on hay that the horse could waste or get too chunky from? Enter the small hole hay net.
(Yes, that is Digby trying to eat a hay net in a stall while he's turned out... Circa 2014.)
I didn't use hay nets, except for while trailering, until a few years ago. I heard they weren't that good for horses because it wasn't a natural feeding position, they're hard to fill, aren't worth it, blah blah. Digby has become a slightly harder keeper every winter and most barns aren't totally thrilled with me to be asking for free choice hay 24/7, because again, it costs a lot of money. I also learned more and more about ulcers. I started using them in 2013 and haven't looked back. I feel like the pro's outweigh the con's here. The barn gets to feed the same amount of hay, it takes Digby much longer to eat aforementioned hay, thus increasing his health and lessening my anxiety. He also doesn't waste any, where as before he regularly stomped hay into his bedding.
If the barn says, "it takes too long to fill" or "it's hard to fill", please show them this video. Problem solved. You can use a garbage can, a muck bucket, or really any large tub. It's almost as easy as throwing hay.
Full disclosure: Digby DID get his hoof caught in his small hole hay net a few weeks ago. It only happened once ever and he's used the hay net for many years with zero problems. He's the type to paw at his hay and grain when eating and does wear front shoes. I'm not sure if it was just tied too low that night in his stall or what exactly happened. Please make sure all hay nets, even small hole ones that you would think they couldn't possibly get caught in, are tied at an appropriate height. (Digby was fine, for the record. He was freed from the net right after it happened and went hay net-less for the evening just in case he thought it was fun and wanted to try again) I'm still a fan, even if my silly horse decided wrestle with his one evening.
Moral of the story: Small hole hay nets keep boarding costs low and hopefully ulcers away.