I thought his explanation about the blade being knocked clear of the work piece seemed wrong if he was cutting dead on centre but i gave it a try anyway
He is right. The problem is that a parting-off cut requires considerable cutting force, enough to bend the machine (tool post top-slide cross-slide etc.) . The geometry of the machine means that as it bends it pushes the tool further into the job creating even more cutting force - a vicious circle that, with a parting blade*, usually results in a stall ,broken blade or worse.
Changing the direction of the cutting force, either by cutting in reverse (watch that chuck!) or using a rear mounted tool-post will bend the tool away from the job.
There are parting-off versions of the ancient spring-tool design that can do the same automatic backing off task.
*Chatter is caused by something similar. Chatter occurs when the tool springs back out of the work as the thicker chip breaks. The combination of springiness and mass of the machine parts, means that is plunges back into the work and so the cycle starts again - only reducing the cutting force will stop the cycle so oil, reducing cutting speed, changing cutting edge etc, will help to stop the chatter.