I came across the Insert Default Values when I taught a SQL class, many years back. It was an odd way to start a chapter on data modification statements. It is mostly useful for trivia contests, to be honest.
The best explanation I can come up with, for where it might be used, is in a situation -- like a call center -- where you want to latch an identity, but don't have enough data to fill in the blanks. There might be some uses around logging, but usually there is more to be recorded.