I am sure there are more, but here are the obvious benefits that we came up with over a pot of tea and some toast!
- no steel used, so avoid the carbon emissions of producing shoes and nails and transporting them from Malaysia, where apparently most are made;
- barefoot horses don't need glue on or plastic shoes, either, so fewer toxic chemicals as well as carbon;
- reduced carbon emissions from gas too, as trimmers, unlike farriers who hot shoe, don't need to use gas to heat shoes;
- trimmers travel lighter than farriers, so reduced fuel for vehicles;
- on a track system, fields are less poached and have better biodiversity, and allowing grasses to mature for a hay cut is better for some rare insects too.
I don't know if we'd be allowed extra points for the fact that barefoot horses don't make quite such a racket when trotting down the road as shod horses do, but its worth something, surely :-)