In hunter championships and hunter derby’s it makes you look nice but it’s not required but in dressage it’s required
As far as I understand it’s about the level you are competing. Eg. a hunter Championship you wear a Shad, in dressage Advanced and up a Shad is required. All senior FEI dressage classes require a Shad 😊
Also why do some people where shadbelly coats in hunters and some don't? Is it required or not?