Turns out IBM offers pricing based on the fraction of the CPU you actually use. (This requires licensing some compliance software from Big Blue’s Tivoli unit.) This can help push customers onto larger, higher-margin servers, while also reducing customer’s administration costs, since they can reduce the number of machines.
In practice, users must run a script on their machines, and submit monthly reports to IBM. To get an idea of the level of complexity involved, visit this site.