If you ever added Output Queries Debug (http://www.oscommerce.com/community/contributions,2575)
to your site you will have noticed a number of very similar queries getting the parent_id of categories on index.php where you have subcategories showing (two for each subcategory).
Half of them are the same. They are all queries originating from the function tep_get_path.
This mod will eliminate all of those queries.