Answer:
The primary concerns involve employee safety and likely breaches of internal controls.
Regarding safety -- a cash-handling facility with only two employees present is easier and more desirable to rob than one with more employees (read "witnesses").
Regarding internal controls -- it's common for employees working in this type of environment to become (and remain) "sloppy" with passwords, cash, vault/safe combinations and other controls. If a "mysterious cash disappearance" occurs, both employees can expect to lose their jobs.
First published on BankersOnline.com 6/2/03