Not OP, but I have also been curious of the popularity of the actual set of transactions that serve utility and result, or facilitate, an exchange between two a

Not OP, but I have also been curious of the popularity of the actual set of transactions that serve utility and result, or facilitate, an exchange between two actors where one of them is providing something tangible (i.e, transactions other than acquiring cryptocurrency to hold, and then exiting back to fiat after some period of it). Obviously this will be difficult to actually know, for reasons that it's "hard to trace" but also most studies are likely biased in one direction (for the concept of cryptocurrency) or the other (against the concept of cryptocurrency). My intuition tells me that most transactions (at least in absolute fiat dollars) that result in an exchange of tangible assets are largely illicit transactions that would otherwise be frowned upon the individual's place of residence (e.g., ransomware, drugs, money laundering), but I don't know how that compares to other forms like standard retail services, local inflation hedging, or overseas transfers. The former group (in particular ransomware) is certainly enabled significantly more due to the existence of cryptocurrency however.