We basically had a single table that we wanted to be able to nest on itself arbitrarily. Think categories and subcategories, maybe 100k nodes/rows
Postgres worked fine but cypher is so much more expressive and handles stuff like loop detection for you, neo4j was much easier to work with. Performance wasn't ever really an issue with either.
We have something similar in Postgres but IMO disconnectedness also plays a really big part in this whole calculation. We actually ended up just changing the transitive closure for fast operations (and simpler code).
Postgres worked fine but cypher is so much more expressive and handles stuff like loop detection for you, neo4j was much easier to work with. Performance wasn't ever really an issue with either.