Taking into consideration the balance of form and function only helps a designer to achieve his or her ultimate goal: the ideal user experience that conveys the intended message through the seamless form and function of the design.
If a site looks good but no one can figure out how to access the information or art, then how can it be considered a success? Yet, there can't be function without some concept of form. The essence of function relies on form, i.e. buttons and navigational elements need that form to convey to the user that they have a purpose, a reason for existence.
Success is a solid balance of form and function to deliver the envisioned idea and to generate the ideal user experience.