The Old Shell Game
usage-based billing is non-deterministic
The cover of non-deterministic token consumption is a wonderful umbrella for all sorts of potential billing shenanigans ("revenue enhancement").
Back in the day, we were charged for mainframe computing. CPU seconds, lines printed, cards read, cards punched, terminal connect time, permanent storage used.
But the rates for each of those were published, so unless you did something foolish such as setting a very high CPU time or line output limit on a job which had an infinite loop bug, you weren't surprised when you got your bill.