When set to Code, any Column element will display raw html while Visual, WYSIWYG editor instead. This option could be set globally and will be applied to all Columns. In both cases, shortcodes are allowed and being parsed on the fly, so there is no need to reload the page.
Moreover, this option is set for account what means that developer working on same site may use Code, while site owner who is beginner, WYSIWYG editor. It gives great opportunities for people with different preferences to work together on the same website at the same time.