As a UC Berkeley student, once your dissertation is submitted electronically through the ProQuest online administration system, it will thereafter be published open access online in eScholarship.
UC's system-wide Office of Scholarly Communications explains more about this process generally (check out their Open Access Dissertations & Theses page). For the UC Berkeley-specific publishing protocol, please review the Graduate Division's Dissertation Filing Guidelines.
Making your work available to be read online immediately in eScholarship or ProQuest has many advantages.
First, it clearly establishes when your work was created and published, which are powerful resources in preventing or combating plagiarism. Others will be able to discover your prior publication.
Second, it can help build your academic reputation. Once your dissertation is published open access, researchers around the world will be able to read and download your work, and can begin citing you in their own publications. (Check out these studies on the advantages of open access publishing on citation.) Citation of your dissertation by others can be offered as evidence of research significance in employment reviews.
For more on the value of immediate open access, please see:
UC Berkeley Graduate Division's guidance letter, in which they explain that, "Knowledge of the work of younger scholars may be increased by promoting discovery beyond limited professional networks." Likewise, research available through searches on the Internet can promote professional contacts international in scope and interdisciplinary in reach.
There's a great overview of the value of publishing dissertations open access in
Embargoes are a delay in making your work available online. You should consult the UC Berkeley Graduate Division's Dissertation Filing Guidelines for an explanation of when embargoes are appropriate.
You may wish to consider embargoing when publishing open online immediately would risk "disclosure of patentable rights in the work before a patent can be granted, similar disclosures detrimental to the rights of the author, or disclosures of facts about persons or institutions before professional ethics would permit." (See the Dissertation Filing Guidelines linked above.)
Certain publishers in particular disciplines may consider dissertations to be prior publications, and/or limit their consideration of a subsequent manuscript based on the dissertation for a first book deal. Some authors may therefore wish to embargo due to concern that open access availability of their dissertations will impact consideration of subsequent publications that they base upon their dissertations.
Note that this is untrue for the great majority of publishers. To the contrary, academic publishers typically view prior open access publication as a means to improve acceptance for a book deal due to increased awareness of your work. While numbers vary significantly by discipline, a 2013 study on electronic theses and dissertations indicates that more than 90% of university presses will consider an open access ETD for publication. (See also a 2011 survey supporting the same.) Keep in mind, too, that your dissertation will be revised and rewritten significantly if/when you shape it into a manuscript for a first book. Most publishers accordingly view this as entirely new work.
You should check with your advisors and the field of publishers you are considering about their recommendations. It is important to familiarize yourself with the policies in your field.
As a condition to graduation, and in support of the purpose of graduate education to make your work available for other scholars, UC Berkeley's Graduate Division requires that you make your work available online in eScholarship. (Again, please review the Graduate Division's Dissertation Filing Guidelines.)
As with any other copyrighted work, other scholars can make fair use of your dissertation in their own research. Since you own copyright over your dissertation, however, you can decide whether you want to license your work beyond what fair use already allows.
There are several reasons why you might wish to license your work. One reason could be to contribute to knowledge building and scientific or artistic progress. Certainly, people can already make fair use of your material, but by licensing it you are encouraging thus facilitating their use of your work. Another reason might be that making it easier for other people to use your material could translate into them using your work more often--which means being cited more often, and increasing your scholarly impact and profile.
On the other hand, some publishers might treat your dissertation as a prior publication, which you might not want to license even further than fair use already allows.
So, before you decide to license your dissertation, consult with publishers in your field and your dissertation advisors to assess whether licensing could impact your ability to secure a subsequent first book contract. Usually your first book is substantially different from your dissertation after significant required editing, but it is always best to explore the contours of publishing in your discipline.
If you do wish to license your dissertation, one option is to use a Creative Commons license. Creative Commons licenses allow copyright holders to prescribe the scope of uses (beyond fair use) that others are able to make of their work--while still retaining copyright ownership for the creator (that is, you are licensing your work for others to use, not transferring your copyright ownership).
If you choose to use a Creative Commons license, be sure to make the selection both in ProQuest and include a notation on your copyright page in the dissertation, itself, that your work is being licensed. This way, when people find your dissertation on eScholarship, they will see a "badge" showing the license, and will also be able to refer back to the written license in your document, itself.