Three main reasons:
~~ The more faces, the more fun. Gathering as well as viewing with each access users rank as one of the best aspects of FaceGuard.
~~ The more faces, the more difficult for any else but you to access. There are 96 letters, numbers, and symbols accepted in the NIST character set. Everyone knows what they are. It’s true they can be scrambled in tremendously intimidating combinations and each additional space increases the access challenge significantly. However any string of known characters can be cracked given time, money and technology. By contrast, humans recognize hundreds if not thousands of faces from their life and there is absolutely no way to know for certain which faces anyone recognizes nor those chosen for Personal faces.
~~ You gain points the more faces you add, as well as how diverse and obscure they are, plus you get points and badges for sharing faces with friends and family.