I'm of the opinion that Agile(Big A) is very useful for creating a system between companies. When something is an agreement between companies you need some agreed and consistent method of working out what happens when and enforcing that afterwards. Agile is much better in these circumstances than waterfall.

Comparatively, in a startup or internal development project in a software company there is much more of an ability to not deliver a particular feature or spend more hours on it.

A startup is likely to find Agile far too slow; whereas, corporates are scared by how fast and fluid it is.