Regenerating counters allows you to clear up problems that may be caused by directly inserting data into the database, or which in some cases may even result from normal usage. When categories are moved or you change the template code for displaying subcategories, you may need to regenerate categories.

Regenerating categories is the most common process you may need to go through. When you have many levels of categories and you change a category name, it will require regenerating categories for all of the subcategories of this category to properly update their 'parentnames' field to display the changed name in the navigation. If you're using mod_rewrite with category names, this becomes essential to keep the paths up to date -- without the regeneration, you would run into dead links in trying to navigate back up from below the category.

Any direct insertion of data to the database, such as if you're importing from another articles script, will require going through all the regenerations: articles, categories, comments, members, category selector and totals.

Note that regenerating totals is useful if you ever suspect that the number of articles, categories, etc listed on your main page is inaccurate.

Regnerating the category selector / sitemap is sometimes needed to keep display of subcategory data on the main page (or anywhere that info from 2 levels deeper than you're at is shown) up to date.