When you buy a video game you might find that it could get resold after you have gotten tired of it or perhaps you have mastered it.
Perhaps you or your child no longer wants the game and would like to sell it. Both you as the seller and the person who would buy it would want a bill of sale.
This receipt for the sale, is crucial to prove your ownership. It also tells who you sold it to if that comes into question.
Buyers will have more confidence when getting that piece of paper in hand as a receipt for the money they handed over and to show ownership of the item.
One form can serve for items that are part of a series or group collection although it might be suggested that for many items, multiple forms would be more appropriate.
If you are a buyer and you feel that the seller has only some generic receipt book type sales slip for you, then you may want to ask the seller to fill out your bill of sale so as to have better documentation.
As a seller, it is a good idea to instill confidence in your buyer so that you will have an increased chance at doing more business with that buyer.