If said that you would like to search for aggregation project, based on drupal 5.

You enter your search, and select 5.x in drupal core compability, and tick project. it will return no result.

so, i think it is good to have the ability to allow people to search the functionality/natural of a project for certain drupal core version without going thru every single project in one category. (like for instance, the content_display category you have over 170 projects.)