There are several reasons for the choil. It makes it easier to sharpen, a spanish
notch is supposed to be usefull in a fight(not sure how) and it helps make the blade better at delicate work by allowing you to choke up on the blade.
Don't let the classic bowies fool you they were serious using and fighting knives.

"if you want to be a hero you have to learn to drive stick"! Sara Conner