JS,
I would suggest that small airfield codes are all a lot more useful now that computing is taking over!
For instance, a popular flight from here (Strathaven Airfield) to Bute, appears in a flight plan - mandatory and now in a computer based format if one wants to transit controlled airspace - as from XXXX to XXXX.
Not very helpful!
Small unlicensed airfields now have a surprising number of users. To put it bluntly, most big airports with ICAO codes in central Scotland just don't seem to want private flyers, so they have had to move elsewhere.