Currently, process builer run on "Insert / Update" event and not have "Delete" action. I have faced multiple scenarion, in which we can use process builder instead of write any apex code. But, in some cases like "Delete" event we forced to write apex class. If process builer come with "Delete" event then it will be easy for many users. We developers and admins can use process builder in multiple scenario with "Insert / Update / Delete" action.