In my mind, the choil is purely a stress relief, everything else is just a secondary benefit.

I think the Spanish notch was to allow you to catch and break the tip off an opponents blade- if you had the bottle to try it! If you were fighting a person with a rapier mabe you could break their blade..

The reason I put a choil on the knife I made was to make sharpening easier.
That way you could sharpen right to the end without mucking up your plunge cut.