Character Analysis
Elphias was an old friend of Dumbledore's. When we meet him at Bill and Fleur's wedding, he's just written a piece in the newspaper about the late headmaster, and so Harry tries to pick his brains/memories for insights, history, etc. about the dude.
It couldn't hurt, since Harry really felt like their friendship was interrupted abruptly, and he's having a hard time figuring out what Dumbledore's larger plans for defeating Voldemort were.
Unfortunately, the only thing Harry really ends up learning from Doge is that he knew even less about Dumbledore than he realized:
HARRY: You obviously knew Dumbledore well.
ELPHIAS: Well, I certainly knew him the longest. That is, if you don't count his brother, Aberforth, and somehow, people never do seem to count Aberforth.
HARRY: I didn't even know he had a brother.
ELPHIAS: Ah, Well, Dumbledore was always very private, even as a boy.
So, Elphias doesn't really do much to enhance Harry's knowledge or confidence that he's on the right path on this journey he started with the late headmaster but has to finish alone.