When authors produce original works (articles, books, sound recordings, etc.) they are automatically granted copyright protection for that work. Authors hold these rights until they transfer them to another party in a signed agreement.
These rights include:
The copyright owner(s) may transfer or license one or more of these rights to others for a specific period of time or in perpetuity. In the case of works created by employees during the course of and within the scope of their employment, the employer is considered to be the author. Section 101 of the U.S. copyright law defines such work as "work made for hire."
Traditional publishing practices have required scholarly authors to give up all copyright to the publisher of the work. In the past, authors had few options except to sign these agreements. By doing so, they generally gave up the right to distribute copies of their work to classes, post original works on class web pages, share copies with colleagues, post to personal web pages or institutional repositories, or reuse a portion in future works. An exception to this would be “fair use".
When you, the author, sign away your copyright, you lose control over how your work is used. The copyright holder now controls the future of your original work.