I think it really depends on your horse. There is a horse at my barn who paces and runs in circles when she is alone. But I also know someone who only has one horse that they keep at home and he is amazing!
I think every horse should have a pasture buddy because horses need other horses they are herd animals ,and I would be so bored if I didn't have a friend being out side and in all day😂 But I totally understand its expensive😬
My neighboors horse HATEEESSS other horses with a passion but that comes down to not being bought up with other horses ( she was rescued from being beaten ) and some people might not be able to afford a second horse
If you go to shows it's easier for the horse to get comfortable if you keep them with horses at home compared to them being by themselves and being afraid of other horses at shows. Also horses can become aggressive to other horses and if you decide to put them with other horses they may attempt to hurt the other horses. Just my personal opinion.