For me, farrier visits are easier done at my farm than at the boarding stable. My farrier's known my horses for years, they all stand like angels, so he'll do them at home alone if I can't be there. The barn, OTOH, I either have to meet the farrier there or pay the barn for someone to hold for the farrier.
I'm boarding Conjure right now so he and I can have lessons with a trainer who works at that particular stable. (I don't have a trailer and I live too far away for the trainer to come to me.)
In addition to the things mentioned above, I like the opportunity to introduce Conjure to things he'd never see at my place - like little girls turning flips off the tongues of horse trailers, for example.
Or just coping with the distraction of other horses, riders, etc. Very good for a horse who's used to the isolation of a quiet farm.
And it's nice to not always have to ride alone, which I almost always have to do at home.
But I miss him like crazy. Even though I can go see him anytime I want, and he's only fifteen minutes from my office - he just doesn't really seem like "mine" while he's at the boarding stable. I'll be really happy when it's time to bring him back home.