Most archival documents are primary sources, for instance, original records, private letters or unpublished works of art. The result is that information comes directly from the source, meaning it is not subject to interpretation from another researcher. You can find nuances or unexplored facets on your topic by looking at original sources. Another advantage is that archived sources are not widely used; they are often housed in restricted areas of the library or in private collections. Accordingly, you can bring new information to your research. You can also explore ideas that have not been over-interpreted.
Archives often house works of art, writings or film that were not released for various reasons. Sometimes government restrictions, a death, author preference or copyright issues prevented the document from being released. Particularly in the case of authors, unpublished works provide insight into the writing process and insight into ideas and inspirations the author did not choose to pursue. Archival films can create an unadulterated snapshot of a period in time or location. When working on a post-graduate project or manuscript, you may be able to request special permission to view sources which are usually kept out of public access. Using these sources lends professional and academic credibility to your work.
Many archival sources have never been copied digitally. By using them in your research, you preserve the information for future generations. You also have the opportunity to introduce others interested in your field of study to the documents you've discovered through a citations list or annotated bibliography. Some libraries may allow you to make copies of your sources. However, many of the sources are extremely old and delicate. Handle them carefully. Studying protocol in archival research will prepare you for further exploration.
Maintaining and gaining access to archives is expensive for libraries. Libraries work to make sure that old documents and paintings do not degrade. By using archives for published works, or for theses or dissertations for prestigious research universities, you emphasize the importance of the documents for education.