The French Guillotin was created as a more efficient and humane form of execution. Someone swinging an axe could miss their mark and have to take more swings. The guillotin eliminated that possiblity.
Interesting fact about the guillotin: http://www.history.com/news/history-lists/8-things-you-may-not-know-about-the-guillotine
I apologize for it being so short, I had to fit it to my print area.