The main purpose for the Header / Footer Areas section is simple.
This section helps you add scripts or stylesheets between the <head> tag and/or add scripts after the </body> tag on your whole site without needing to edit WordPress theme files and navigate through the code. It is not only efficient and faster to have access to this from the backend of your website, but it’s less intimidating.
Global Website Head Area
You can add any external/internal stylesheets or scripts here and they will output between the head tag.
Global Website Footer Area
Mainly for scripts, any scripts added here will output after the closing </body> tag.