I disagree! Only shut it down if it starts getting too hot or has a leak or some other major issue like a noise. Most wear happens on startup. The purpose of cam break-in is to establish the proper wear pattern which requires plenty of oil and engine speed to make sure the lifters are rotating. Every time you crank it to start it, there is little oil on the cam lobes and you run the risk of metal-to-metal contact. That is why you put cam lube on during assembly. Once you've run it for a few minutes, all of the cam lube is gone and you are relying on whatever oil is between the lifter and cam lobe on subsequent startups.
I flattened one cam when I was a dumb kid in the 80's. A few years later, I became a machinist and built hundreds of engines in my 10 year career and never had a cam failure.
Lee
1966 Barracuda, 340 4 speed