When an object is deleted through the UI, if that object has child objects and/or related entities (Time Entries, etc.) it should be an option to delete them as well. Ideally if no child or related objects exist, the delete would just occur; if they did a dialog would be displayed prompting the user to “Delete Related Objects?” (or language easier for users to understand, perhaps).
There is already a dialog when an object has some related entities (Time Entries, etc.) so ideally this dialog would be modified to list the types (and perhaps counts) of related objects with a checkbox to cascade delete one or more of them.
For extra points, the related object count should be a hyperlink to the list of related objects (but that's not in any way essential).