I think is a specialized vocabulary,Where did your see it?

serve function = the function of a thing and what it serves for This cup serves as a tea-cup. The cup's serve function is for having tea. Sounds like sales jargon. if you're selling something, it needs a serve function - what it is for - otherwise no one will buy it.

serve function= to serve a purpose, role, or function; Example:"The tree stump serves as a table"; "The female students served as a control group"; "This table would serve very well"; "His freedom served him well". http://www.answers.com/topic/serve-function