The ones named above (wrongly logged job in case of printer hardware failure, and so on).

In reality, CUPS counts the job pages that are being processed in software (that is, going through the RIP) rather than the physical sheets successfully leaving the printing device. Thus, if there is a jam while printing the fifth sheet out of 1,000 and the job is aborted by the printer, the page count will still show the figure of 1,000 for that job.

All quotas are the same for all users (no flexibility to give the boss a higher quota than the clerk) and no support for groups.

No means to read out the current balance or the “used-up” number of current quota.

A user having used up 99 sheets of a 100 quota will still be able to send and print a 1,000 sheet job.

A user being denied a job because of a filled-up quota does not get a meaningful error message from CUPS other than “client-error-not-possible”.