The copyright is a law that comprehensively protects intellectual property.
For authors it used to be quite complicated, to allow certain uses, while keeping other rights.

Free Licences allow the authors more control over the usage of their content.
With the well known Creative Commons licences  authors have three basic decisions:

• Allow adaptations of your work to be shared?
• Allow adaptations only if released under the same licence?
• Allow commercial uses of your work?

With the help of a tool on the Creative Commons website  it takes a few seconds and clicks to find the right, valid license for your creation.

This little video explains the concept:

 

So free (or permissive, public domain, copyleft) licences  are an easy way to allow sharing and using of your content.

Wikipedia surly is poster child for the successful employment of creative commons licenses.
The English version alone has nearly 5 million articles under a CC-BY-SA license.

It seems obvious why these licenses help the public and the greater good.
Why authors can also benefit from them will be covered in a later article.