What is the purpose of dissertation embargo periods?

An embargo effectively withholds your dissertation from being placed on your institution's open-access dissertation archive (from which anyone can view/download your dissertation).

I have placed an embargo on my dissertation so that I may attempt to get a few more papers published without my dissertation being searchable on the web. It is a common practice in the department where I did my PhD (though, I wondered sometimes if it was really necessary).

For a more complete list of reasons why one would choose to place an embargo on their dissertation, I'm listing here an excerpt taken from a University of New Mexico page:

Embargos may be appropriate for authors 1) who are seeking patents, 2) who want to publish their work through a traditional press that considers open access publication to be equivalent to prior publication, 3) who have published material from their work with a publisher that does not allow open access release for a certain period of time, or 4) who need to protect sensitive data or information.

A "dissertation embargo" means that access to the dissertation is restricted for a limited period of time (typically one or two years, but possibly longer).

Possible reasons to embargo a dissertation include:

• You would like to patent some of the work described in the dissertation. The published dissertation would constitute prior art.
• The dissertation includes data covered by a nondisclosure agreement for a limited period of time.
• You intend to publish the dissertation as a book, with a publisher that restricts consideration of manuscripts based on publicly available dissertations.