Subgraph vs Group

I see the option for using Subgraphs in OG Pro. But why? I can repeatedly group items and it appears it is the same thing. What is the advantage to using a SubGroup?

Collapse and expand.

But you can do all those under Groups. What advantage does Subgraph give you?

Tested out in a ‘scrap’ document. Kind of nice to help simplify a complex diagram. Would be nice to be able to double click to open/close.