In talking about switching operations with my friends that are professional  railroaders, one recurring topic that keeps coming up is the importance of setting hand brakes.  When a locomotive cuts away from its train to handle a switching move, the hand brakes on one or more cars on the now engineless train need to be set.  Wouldn’t there still be enough pressure in the line to hold the cut I  asked?  Maybe, they responded, the rules are that you set the hand brakes regardless.   When spotting a car or cut of cars at an industry the hand brakes on the car(s) must be secured before leaving.  Obviously when pulling cars from an industry the brakes need to be released first. 

Here’s a video showing a conductor securing the hand brakes on a car.