The disadvantage is - it's easy to abuse it ! Some companies
allow anyone to use their franking machine - meaning that any
employee can frank personal mail, thus avoiding paying for the
postage. Franking machines are 'loaded' with pre-paid credit. Once
the machine is 'primed' - anyone can feed letters through it - and
use the credit until it's exhausted. That's why most franking
machines are locked away until the end of the working day, and one
person franks all the outgoing mail.