If done correctly what you teach on the ground transfer to the saddle. It also makes for good ground manners.
When we teach Groundwork at an early age the transition to a well rounded saddle horse is achieved much easier. The first ride is a great experience for both the horse and rider.
When you have built confidence in the horse on the ground you can introduce objects on the ground. It allows them to process what the object is and know that you are the confident leader to take on the new object.