Good CAD/CAM software will detect obvious errors in the toolpath, but there are things that require common sense. A large proportion of machine crashes are caused by a discrepancy between the computer model and the real state of the machine, which the software is obviously unable to detect or prevent. CNC machines generally have no sensing capabilities; they rely on the operator to provide accurate measurements on tool height and work positioning. A transposed digit or a value entered in the wrong field can easily cause an ugly crash.

Workholding is a common issue - a 3D model just floats in abstract space, but a real part needs to be securely held in place. It's quite easy to inadvertently crash a tool or spindle into a clamp or vise, or to apply cutting forces that exceed the clamping force and throw the part.

https://www.youtube.com/watch?v=PsFNeiAu04M