Balance is key to playing all sports, golf in particular. In fact, the PGA Tour logo pays homage to the traditional finish. While current players rarely strike this pose, it contains a couple of key truths.
At the end of a correct swing, the player will be standing on one foot, but he/she can use counterbalances to improve their form. The tip of the back toe is one counterbalance, while the club position is another. You can draw a diagonal line between the back toe and the hands. These two points offset, helping the player to remain in balance.
Often you will see players continue the hands around the body and past the head, but this can be harmful. It moves the balance point of the hands backward, meaning the player has to adjust somewhere else. This usually comes at the expense of maintaining correct posture through the swing. The player becomes more upright at the finish, which can lead to topped shots if the process begins too early.
It's a good idea for beginners to mimic the PGA Tour logo before getting too fancy with their finish.