The way that I understand it, is by including an OWP at the same time as an Inland application, it gives the person implied status, provided they still have legal status when both are received by CIC. An Inland applicant is not eligible for the OWP prior to AIP, so the implied status simply keeps them in a legal status, per se, in case their visitor visa, WP or Study Permit expires before they get their PR. In many cases the implied status does NOT allow the person to continue to work.
It is now the pilot program OWP that enables an Inland PR applicant to receive one prior to AIP, as long as they have maintained their legal status. The person must have legal status when the pilot OWP is received by CIC for it to be processed. If they do not, they must wait for AIP before their OWP would be processed.