My title pretty much says it.
One of the really common things I see when people demo knife (offense or defense), even in most FMA's, is a lack of discussion about controlling range. Tim Waid, who is the head of the PTK organization I train under likes to ask "how did you get there?" when those super sweet videos are posted of people doing cool stuff with the knife.
In the video above, while you don't see much in the way of lateral movement or use of the triangle, you do see the importance of range. One should also be able to see why medium range with the knife, is so dangerous. There are ways to attack your opponent, particularly their hand, without being in position to get hit yourself. If you do go inside, get in all the way. If you are going to stay out, get out all the way. Medium range is a range to bridge through, not a place to hang out.