To be able to send the horse through tight, narrow spaces (without moving your feet) at both a walk and trot and have the horse yield and face you, and then go back in the other direction.
Horses are actually naturally claustrophobic. Some more than others. Wether the horse goes between you and a fence, through a gully, between fences/through gates or just between two close objects. So sending them starting off the fence and making that space smaller and smaller helps get them over their claustrophobic.
It also teaches them to be lighter in the halter, that halter pressure behind they're ears. They should be able to go in the direction just by me pointing that way.
And lastly it's also very useful for trailer loading. Being in a big box like thing that moves can be really scary for a horse.
Teaching this exercise to a new horse that has never done it was a challenge to me. I was teaching a horse named Rose at the time through some of the fundamentals awhile back. Some horses will have a hard time learning certain exercises and sending was one Rose and I had a hard time on. In fact it was very frustrating! She just didn't seem to get what I wanted her to do. But it was also fault too..
From what I can remember I was asking her to step between me and the fence in a space too close too early. I didn't start at a good starting point. I should of took a few steps back and have her go between that. I can definitely remember her being a very claustrophobic horse, very unlike Ruby and Sugar. I don't remember either Ruby or Sugar ever being very claustrophobic.
My other problem was not adding enough pressure. She would start by going forward but as soon as she realized how small the space was she would back up...and back up, and back up! I followed her like I was supposed to do but didn't add enough pressure. And now that I'm remembering I also think I had way too much loose rope. Which made it harder to reach her and easier for her to back up or try to run off.
When Shelbi (CA Ambassador) was here I asked her to help me with this after we finished with Ruby and Sugar. It was a hot humid day and there was a lot of dust...and I was so tired and sore...BUT it never felt better! We spent a long time, she having me teach the lesson to Rose while correcting any of my mistakes. I did it over and over and over until I could send Rose 5-8 times without a fault either from her or me. It was so tiring but the next day when I took Rose out to teach her the same lesson I don't think she messed up once! I was so excited about this and a little surprised on how well Rose remembered the lesson the day before! I practiced sending her everywhere! I was just so excited she was finally able to do it I was having fun sending her all over the place.
Those times when it's feels SO hard and tiring but as soon as I push through that point it's SO worth going through again!
"Sometimes you have to go through some ugly stuff to get to the good stuff" ~Clinton Anderson
Goofy picture from awhile back of me and Rose: