Categorizing content helps users effectively find documents within the site. This can be done via SharePoint through the use of custom columns or meta data. Create these columns at the global level of the site collection and add them to the required content types. The document libraries or lists associated with these content types will then inherit these custom columns.
These custom columns can also be set as required fields. For example, you may include a column identifying the Sales Territory a document is related to, making it easier for the Sales staff to filter their search results quickly by their relevant territory. This also improves the ranking of the search results.