The DNA matched me up with a living 4th cousin. She had information on our common great-great-great-grandfather and information that our gg-grandfathers were brothers that had been passed down in her branch of the family but was not available from anyone else. Up until that point in time, I had been unable to identify the parents of my gg-grandfather.
So I have been able to identify my very long deceased ggg-grandfather. Later this year, I will conduct Y-DNA testing on straight male line only descendents (my brother and a male descended from my gg-grandfather's brother) to further confirm it.
Until I had this autosomal DNA information, I would have been unable to identify anyone for a Y-DNA test.