The horse is being worked without the weight of a rider. Work in Hand aims for gymnastic and further training. It is very well suited for horses which can not (yet) be ridden.
You can teach your horse everything: tempi- and pace-changements, lateral work, piaffe, passage and and and…
The rider learns to pay attention to details of a lesson, to give the correct aids in the exact right moment and improves his own endurance, patience and coordination.
Next: Work on long reins