The minimum quality is the one below which one wouldn't gain any operative gain (in "readiness") for the pictures he's going to take.
The maximum quality is the one above which one wouldn't gain any visible quality gain for the final use he's going to make of the picture.
The quality of a Microfilm Minox was not low for the intended purpose so "Cicero"*, the Turk spy, was right in using it.
On the other hand taking pictures for news with a LF camera pays a price in "readiness" and does not give any advantage in marketability.
In the stock photography milieu there is, it seems by reading some forum, a tendency to favour APS-C or Micro Four-Thirds mirrorless cameras to gain "readiness". The little amount of quality one has to let on the table is a little price to pay as in stock photography good enough is good enough (more than that is very rarely leading to a sale, subject prevails by a large margin over technical quality).
* Elias Bazna, or Elyesa Bazna, or Iliaz Bazna in Albanian as he was an Albanian of Kosovo.