To study the purpose of designs, beyond individual goals (e.g. marketing, technology, education, entertainment, hobbies), is to question the controversial politics, morals, ethics and needs such as Maslow's hierarchy of needs. "Purpose" may also lead to existential questions such as religious morals and teleology. These philosophies for the "purpose of" designs are in contrast to philosophies for guiding design or methodology.
Often a designer (especially in commercial situations) is not in a position to define purpose. Whether a designer is, is not, or should be concerned with purpose or intended use beyond what they are expressly hired to influence, is debatable, depending on the situation. In society, not understanding or disinterest in the wider role of design might also be attributed to the commissioning agent or client, rather than the designer.
In structuration theory, achieving consensus and fulfillment of purpose is as continuous as society. Raised levels of achievement often lead to raised expectations. Design is both medium and outcome, generating a Janus-like face, with every ending marking a new beginning.