Let's say you have an e-commerce site that sells to multiple countries and all the pages are written in English but you sell the product in different currencies based on the country the user is buying from. In this case, since all the product pages are English and the only different is the currency that is changing, Google suggests you do not make country specific pages and use hreflang in this case.
Here are the tweets:
Google folds pages together if they're identical, so either make them unique, or just make one English version. (Don't overcomplicate it.)
— Google Webmasters (@googlewmc) October 24, 2017
You can see the webmaster is describing the pages as being "all English" but the only difference is the currencies on the page. Google responded, "Google folds pages together if they're identical, so either make them unique, or just make one English version." "Don't overcomplicate it," Google added.
If the pages were in their country specific language, then sure - but just for currency changes, it seems Google is saying don't bother because Google will just fold them together as one page anyway.
Forum discussion at Twitter.