DRV10975: DRV10975Z - VREG pin zener

Part Number: DRV10975

The datasheet states that a zener diode is required on the VREG pin when using the internal regulator in linear mode.  What is the purpose of the zener diode?  Is it really required?

I ask, because I have an application where I left off the zener diode, but the voltage on the VREG pin still looks just fine... voltage is stable, no spikes or overshoots.  Is there a particular condition that could cause the internal linear regulator to overshoot and damage the internal circuits?