Most of the LEO uses I know of we're not covered by the news.
Every single situation is completely different with "defensive" use of force, especially deadly force. I know of one particular incident a guy (LE) I train with was in where he took a blade and went ear to ear through the BGs eyes. Of course they were fighting over a pistol and the blade was the only tool he had ability to deploy. No charges not even a raised eyebrow.
It is very rare that a person will use a blade against a person who is not armed. However it is not outside the realm of possibilities.
For LE the blade is a get off me or get off my gun tool most of the time. Especially when considering many cases I've personally seen have a LEO using a blade against the BGs hands which were on his pistol first and then moving on to something more vital, but usually only when that BG doesn't let go of the gun right away