Product Choices can be added when you want your users to choose additional options for the products without affecting product price.
An example would be sauces that could be added to a burger. Or if you were selling a bucket of chicken wings and it comes with a sauce of the customers choice, you can list your sauces here allowing the customer to choose any option with no additional prices being added when they add to the cart.
Once these are added, they will then become an option you can enable for this product for the customer to choose when selecting this product type, they are then able to choose the customization option for their order at no extra charge.