What is the actions table for and can I delete orphaned actions? I just ran

$ drush cc all -v


and it tells me I have orphaned actions. I'm curious to what the actions table is for in Drupal 7 and if it's safe to just drop all the data in the actions table?
There is no button or link or even an indication that orphans exist when going to /admin/config/system/actions.

I don't really get why, but when I visit /admin/config/system/actions/orphan the orphaned actions are removed.  I'm watching the Drupal log when I go to that path and it systematically removes all the orphans.