Ground tying is one of the most useful things that I train all of my horses to do. One of the main reasons that I teach it is so the horse respects my command even without being on cross ties or constantly held. It comes in handy as well, I can tell my horse to stand and can set up poles or jumps, help a student, get a gate, etc... Here one of my horses waits while I set up some poles, I think that I was taking longer than she thought I should, but she still stood patiently :)
Would I recommend going to a show, getting your horse off of the trailer and trying out your technique for ground tying? NO WAY! However, in a safe environment, where if it doesn't work nobody gets hurt is a great way to test your training. I usually teach my horses to ground tie by standing them in the aisle way of the barn with no cross ties and just simply giving the command to STAND. If the horse moves forward or steps backwards, put them back in the place that they started. You just continue this whenever you can, and before you know it your horse will stand like a champ. Anyone ever tried it?