DBDOC shows you all the tagatoms used in your graphics. It also allows you to see the Process Portal B server databases in parallel with the Composer taglists. This makes the task of keeping the two systems synchronized easy.
DBDOC tells you about the tags in your database that are not in any graphic, about tags that no longer exist in the database and tags that no longer have source blocks in the configuration. This information allows you to keep your graphics very tidy.
DBDOC gives you a direct link from the Process Portal B graphic to the configuration CLD / CAD files, making fault-finding trivial.