How do the use cases for exporting data from a SaaS app differ from those for the results of an API call?

Most existing ETL infrastructure—Fivetran, Stitch, Airbyte—is actually all built on top of their sources’ APIs, so the actual data coming out is the same a lot of the time. 

I think the use case is really the more important distinction here: whether you're trying to sync that data for analytics or whether it's more of a transactional use case. 

If you're a customer of a Stripe or a Modern Treasury, you might use the API to initiate the transfer of money and you might use the GET endpoint on the API to check the status of that particular transfer. 

But if you're reporting on the last month of transactions, you'd probably prefer to have a replica of that entire data set in your own environment for analysis. In both those cases, the actual data that is behind the scenes is exactly the same. 

Theoretically, you can find the same data via either method, but the way that it's reported and the model of which it's delivered, I think that's where the big distinction is.

To summarize, it's really about the use case, whether it's a transactional use case or an analytics use case.