Interesting bit about money since it's mentioned in there: Most economics give the same version in the notes which is that money just kind of _sprang up_ out of no where to solve this problem of trade, but it's actually very likely that Credit, and therefore also Debt, is the source of "money". That money only became more important as trade extended from tribes and to strangers we didn't trust. Also that the world goes through cycles of being currency heavy and credit heavy in their transactions of which right now we're living through a new credit heavy cycle which is hard to predict the outcomes of.
I read 'Debt' a few years ago. Am currently reading Niall Ferguson's 'The Ascent of Money' which dives more into the details of how our banking and monetary systems arose. Only two chapters in, but I would recommend already.
Yeah, that narrative isn't new; its being covered in various documentaries and books, including this cartoon [1]
Harari gives very good examples of how money is useful for trade in his book. These examples underline how money is useful for trade. Its downright impractical to trade goods for goods because of multiple factors: fluctuation of value, different values for different people, lack of preference of the item from one of the parties.
Perhaps there was not one reason why money is useful. There surely isn't one now.
Recommend this book: https://www.amazon.com/Debt-Updated-Expanded-First-Years/dp/...