Extract from Aunty Kaye’s Doggy Dictionary of Training and Behaviour
This means asking the dog to move from heel position to the handler’s right side. It is a command or signal given in formal training.
By convention, the dog walks on your left side, known as the heel position. This can become such a habit that the dog is almost incapable of doing anything else. Actually the dog can learn to walk on the other side, but this may be a challenge to traditionally trained handlers, who tend to believe that the heel position is sacrosanct. The exercise of changing sides is taught to Royal Netherlands Police dogs. It has a very practical purpose. The police patrol on bikes and their dogs heel beside them but are taught to come round to the right side to avoid obstructing the footpath if a pedestrian is approaching. This snazzy little manoeuvre is well worth teaching if you ride or walk with your dog along the local bike path.
You may wish to teach it if you do Agility with your dog, because your dog should be able to cope with being on your right or left side as you approach an obstacle.