Non-Free packages.

[Gymnogyp]

In the installation documents, it states that i must have the Debian Non-Free repositories enabled. I run a small hosting business on the side. My questions follow;

1. Why must these be enabled?
2. What packages are Non-Free?
3. Do I need to have a license to sell hosting with the Non-Free packages?
4. To sell hosting, do I need to pay anyone for these packages?

Thanks for answering my questions.