The required and sufficient length of the neck strap is 68cm. I think this is the optimal length when you specialize only in photography. This length is sufficient when holding the camera both vertically and horizontally. I don't think the pointlessly long straps of the past are necessary for shooters like the M-type Leica who concentrate on shooting and don't check the monitor every time, or for modern shooters who use compact mirrorless cameras to check photos on the viewfinder rather than the rear monitor.
