Sometimes you want to license files without people needing to purchase them. Even using coupon codes to make products free still requires them to be purchased through the Commerce Checkout system.
This is fine for physical products where you still want email and address details of potential future clients.
However when it comes to files, users require an account to access their files, so chances are you have all the details for them already. And there is no shipping required so why make them go through the checkout process just to get a license for a free file? (Seriously if you have reasons comment!)
Here is a snippet of how to generate a file license for a user:
Today I learnt the difference between 'license' and 'licence'. Unless you are American (in which case just ignore the existence of 'licence') read this.