I am open to changing my mind and I am looking forward for answers to your question - but I think it is like a click bait - looks interesting - but not really useful.

Mostly to understand the structure of your knowledge base. To search across the KB it is more convenient to use Obsidian/gbrain itself.

Suppose you've been collecting thousands of notes from meetings, feedback from colleagues or code-reviews, "insights" and tips from you wife over the years. Aren't you curious what this KB contains and how it has evolved over time?

So, shortly it is a debug tool for your second brain.

They look cool, but it is known that they don't add much.

In Obsidian, the local graph has real uses, but the global one is mostly to see structure in your notes and look cool on social media.

I was researching and prototyping a graph like Obsidian's before Obsidian came out, based on the ideas in "how to take smart notes"

https://www.youtube.com/watch?v=a6yUA46ek6M

I believe the direction of UI I was exploring there has more than what graphs currently have, although I didn't have the time to build it out and I saw that the site has been offline for a while.

It was a working tool though.