Honestly, I'm done with this picture but I will answer this since it's not a snapping question.
Blinders are designed so the horse is forced to keep looking forward, so it basically blocks out anything that may be dangerous to them.
I don't like blinders, the horse cannot see around it which means, REGARDLESS of how well it's trained, it will have a very good chance of spooking. Especially if a car drives by it fast, you can train as much as you want... that fight or flight instinct is who they are, they will run off a cliff to escape a predator so putting blinders on would scare them if anything they didn't know was there, suddenly appeared...