This is a common accounting control practice. Generally speaking, most accounting fraud is still manually performed and has to be done in person, and relies upon frequent tampering of normal accounting controls and procedures, often monthly, sometimes weekly and even in some cases daily. See the stories on PFGBest for an example.

The idea of enforced contiguous vacation time is that this kind of fraud is revealed when at least someone else has to step in and fill in for the time the fraudster is away. Even if someone doesn't backfill the position during the vacation time, surrounding processes and controls are supposed to pick up evidence of the fraud now that the tampering cannot be engaged.

Basically, no one with control over finance and accounting functions is supposed to be so indispensible that they can only take a few days here and there off. In fact, someone in those roles that makes a big deal out of being able to be away for long is usually a red flag for auditors.

A friend of mine works for a large investment bank and this is the stated reason for their mandatory 2 week continuous holiday.