Are the top use cases for this sending emails for in-product actions or do people also use it for your marketing website too (eg to send a drip sequence when a customer requests a demo)?
It was built for in-product actions but you can use it for whatever suits your needs. It may need some extra code on your side to make that work though.
I am currently using it to check up on my users after they have either skipped or completed the onboarding so it is definitely doable!