I don't know. I feel like NCIS has reasoning for most of theirs
Some of it is purely for shock value, & you could argue are unnecessary, but they still have a reason for it. It generally continues someone's story or the story of the show on. The issue with Emily is that they worked so hard to show she was clean, & appeared to wrap that story up, only to bring it back. But I guess that also shows that not everyone makes it. That one small slip up can cost you your life still.