It really doesn't add clarity :)
Dash vs underscore and use of "item"
cat-item (dash)
page_item (underscore)
current-cat (dash, no -item)
current_page_item (underscore)
current-cat-parent (dash)
current_page_parent (underscore)
(no such class for category?)
current_page_ancestor
Is this a common agreement that page classes should go with underscore? Just my thoughts :)