The free default offer is automatically added to all user accounts as soon as a customer registers. The offer can't be cancelled or removed. The content available in the offer is free of charge for the customers as long as the account isn't deleted.
You can use the free default offer to give access to content that you are not allowed to charge for e.g. public service channels or you show advertisement.
You can also use it to promote a certain type of content. You can change the content in the package connected to the offer. This gives you the possibility to tease your free customer base with new content and use it as an upsell opportunity.
You can read more here on how to create offers in the Magine Pro Console.