If I understand it correctly, the use case is to link existing MD notes visually. That's a different way of looking at the data than the two-way backlink approach that was the foundation of Obsidian (and other personal wiki tools).
I'm interested in this, as I currently use a combination of Obsidian + SimpleMind, but currently SimpleMind has more features (full fledged mindmapping app), and I like having two separate spaces to sketch out ideas.