I've had half partitions in normal 12x12 stables and also stables converted in an old barn with just two massive planks bolted to uprights.
My horses really really loved it, they were able to groom each other over the partitions. Feed times were ok as the stables were big enough to keep all food away for the middle so there was no arguing.
I also introduced a new horse this way, left them in for 24hrs to get to know each other and then turned out with not so much of a squeal.
The yard I'm at now has regular stables and I'm sure my horses miss the closeness.
Can't think of anything for, except economy if you are building them
Against; some horses really dislike being overlooked - one of mine to the extent that she kicked down the dividing wall
You have to be more careful which horses you put next to each other
Any sniffles or other ailments can spread more quickly
I prefer a higher partition between stalls. Half walls are fine, IF horses get on, but if you have a bully, or a greedy feeder then them being able to reach across into the next stall effectively halves the space the bullied/nervous horse has, and that's if it only has one neighbour. I would certainly not build stalls with half walls without bars.
I converted my ex standard bred racing barn prison cells by chainsawing 2' off the dividing walls, and ripping out most of the bars. My stalls have 8' high walls, but the fronts of most of the stalls are about 5' high for the entire width, horses can talk to each other if they want, or not. Their choice.
I'm not a huge fan of half walls. however if I had just my horses and they got on I would have half walls.
I'm currently at a yard with half walls and bars above that and it's the first time I've kept my mare like this (she had a half wall before but she was the end box so no neighbour one side) and she hates it sometimes gets really grumpy with both her neighbours and it can be interesting if she is intent on having a go at one of the neighbours (or vice versa) and I'm in the box! She is pretty good though I growl at her and she will just stand in the middle of the box making faces to either side of her. If I had the choice I wouldn't keep her like this again - full walls all the way.
Another livery has at my yard has just taken down half the wall separating her two horses so they can chat - unfortunalty her youngster has now developed a unhealthy obsession with her other horse - calls constantly if the other is taken away. So the owner is putting the wall back up in the hope of getting back to normal.
ok scenario: big 17hh WB cut late little opinionated turns out with others ok but i have my doubts in this kind of environment. at the moment he doesnt have a neighbour but we have one other livery who is a squeely 16.2 gelding who we hae hacked out with no probs is turned out n field next door at the moment (going to put all out tgether in spring when ground better) but this is his potential neighbour.
there is lots of squealing over the fence and lots of frnt legs striking out
i want at least a grill between the two if not a full partition, for reasons above and also i dnt want him getting attached i dnt want chunks taken out of either of their necks and the other livery is a mate of mine and i dnt want things to get awkward
I have had half partitions - and bars and never again. I hate them. Horses cannot get privacy - they can get paranoid about being overlooked at feeding times. It encourages seperation anxiety as the horse always sees something next to it. All our horses here - 16 of them have daily turn out in groups - 10 hours a day in winter and 24/7 in summer so they have plenty of horse company. we stable horses away from their own field mates so we don't have any that suffer seperation anxiety. Horses that came to us as dangerous in their stables have chilled as theri stable is their own, not over looked, no other horse leaning into it. Far more relaxed than with bars or half walls.
I have full partitions with talk grills for about 1/3 of the length - best of both worlds, because the horses can 'talk' if they want to but they can also get some privacy. Another plus is when the weather is really bad I can close top doors and they still can see each other and get less claustrophobic.
Having witnessed my 4 yr old actually break off part of the wall trying to kill a weanling on the other side then I would have to say no, unless the horses really, really get on.
I would never want \ have wanted half walls for either of mine. My old mare would have killed the horse next door, and my current gelding is a total wimp and would spend the whole time jumping away if the horse next door put an ear back. I have trouble getting him through gates out hacking because the horse whose rider is holding the gate may kick him through the gate (even when the other horse is a 12.2 pony!).
However, I knew two TB's at a yard I worked at, one was a crib-biter and the other box-walked intermittently. They were getting on so well the YO moved them to two boxes she had that only had a half wall and they both completely stopped their 'vices'. They used to play tug-of-war over the wall and generally had great fun. There could be quite a bit of squealing and play-fighting from them too (especially when they were turned out together) but they never hurt each other. They didn't have any problems with seperation anxiety either, but would start cribbing / box-walking within a couple of days of the others absence if one was away for any reason.
I'm a fan for my own, i.e. at our current yard there is a big window with chainlink fencing compeltely covering the 'hole' (so they cant actually put their heads through) between my two stables. I wouldnt like it so much though if it was someone elses horse next door!
I really like it as my two are best buddies - one is on box rest at the moment so its nice for her to have a bit more closeness to Spyder when he is in at night. When I'm mucking him out Ellie stands and rests her head on the ledge and watches me. I would happily take the wire stuff down so they could put their heads over!
my own horses at home i have 2 blocks of 2 with half walls and it works brilliantly if the horses are put in with the right horses and are stables are 15ft sq so pretty big - only prob is if stupid OH puts boss horse next to baby horse then he gets picked on but really he does have enough room to get out of the way but I don't feel he should have to in his stable. When there in their 'right' places everyone gets on great and there often grooming or just standing with their heads over the partition
if it was a livery yard though I think i'd be worried as you dont have the control over whose next to you etc
i don't like 1/2 partitions unless the stables are huge (e.g. mine are 15' x 15') and the horse gets on really well with its neighbours.
my mare spent overnight at vets' recently in a 12' x 12' stable with strange horses both sides, she was really traumatised by it. they have no privacy and don't relax, which i don't think is fair.