Minis do not do rail work. In Model Classes they simply walk into the arena and set up the judges are not allowed to watch how the horse walks meaning if it tracks straight or not.
Many times this is used as a gauge to see what *type* the judges seem to be picking. Although at the National level many exhibitors prefer to not enter this class as the horse would be tired by the time it came to the Open Halter Class.
So if you had a horse that stands correct and has great conformation, but tends to walk a little funny, this might be a halter class that you would enter in?