Not facebook's main functionality. The feature's functionality. e.g if you are building a captcha test feature, it should not keep more data than is needed for

Not facebook's main functionality. The feature's functionality. e.g if you are building a captcha test feature, it should not keep more data than is needed for it to function. This is the policy where I work at least, and I believe this is shared by most privacy-conscious companies (which facebook is... as far as the legal definition of privacy is concerned :)).