Deve you are well on your way to understanding the purpose of the octane selector. The last part of it is that when Chevrolet offered that feature, it was to allow the operator to either advance or retard the timing to account for the wide swing in octane from gas station to gas station, without losing their original pointer-on-the-BB setting.
Carl
Also promoted/provided to assist the driver in situations where the truck was driving at different altitudes. Adjust the octane selector in the different location ("ping" at wide open throttle) and when you get home adjust it back to "normal".
http://chevy.oldcarmanualproject.com/chevyowner/51tom31.htmIf you lived in Ft Collins, CO and had to visit Breckenridge, CO and later visit your mother in North Platte, NE, you would want to adjust timing (and be able to easily return to "normal" timing setting when you return to Ft. Collins).
