Once upon a time, there were just three widely supported netmasks, namely /8, /16 and /24. The generalised netmasks were introduced and debugged because IP address pressure became serious. Before classless networking was generally available, there was still plenty of addresses for us early adopters and there was only spotty software support for netmasks other than /24.

Newham has ten libraries now. During that time, a council that had then libraries and wanted to have have a common loan database would typically use ten almost empty /24s.

I know someone who operated a school system at the time. Many schools had only two IP addresses allocated, namely .1 for the router and .10 for the local server. Each school had a /24, though, because that's what worked without bugs on the software at the time.

Other working configurations did exist. The university where I studied used a lot of proxy ARP. Which was possible, although I heard it caused a fair amount of cross-city traffic. If I had to pay for WAN traffic back then, I might well prefer to use more IP addresses and less WAN traffic.