Allow you to customize menu location and breadcrumb of nodes depending on their content type, associated terms and others conditions.
By this module you can create rules which indicate menu location of nodes (it implicitly influences to nodes' breadcrumb). Rules are stored in database and contains such parts (fields): content type, term ID 1, term ID 2, PHP condition, menu item ID, weight. Rules are applied on review of nodes at full mode (hook nodeapi is used for that).
Use case 1: You have content type "project" and page "projects" with list of all projects. And link to this page "projects" is present at some menu (e. g. "primary links"). When you select project from projects list and view full node presentation your breadcrumb have only one link to "home" page without link to "projects" page. So with help of this module you can create appropriate rule and breadcrumb became "home » projects".
Use case 2: Your stories are classified with help of taxonomy, e. g. "site news", "company news" and "birthday congratulations". And you have 3 corresponding pages with list of stories' teasers (pages "Site news", "Company news" and "Birthday congratulations"). Let these pages are present in some menu(s). And again you can fix breadcrumb and menu location of stories by creating appropriate rules by this module.
For more complicated conditions you can use plain PHP code in rules. In code you must use $node variable, e. g.,
$node->type == 'story' || $node->type == 'news'.
See also comparison of breadcrumb customizing modules in Drupal documentation.