I've had a bunch of crashes with assorted injuries but only once did my
helmet play any part whatsoever.

Type 1: I was out of the saddle accelerating out of a left turn (not
especially hard, just commuting) - left pedal spindle on the downstroke
snapped and I immediately went down and my helmet hit the pavement. I
heard the helmet scrape along the road until my body and bike (still
attached to my right foot) came to a stop. The helmet saved my ear and
scalp and probably prevented my glasses from getting smashed into my face.

It would probably have been my worst bike injury except for when the car
hit me (broken shoulder). Instead it was non-head road rash and bruised
rib.

I'm a believer, not a Nazi.