The fundamental difference of ad interim appointments and regular appointments lies in the timing of the appointment.
Ad interim appointments are made when Congress is in recess and as such, the Commission on Appointments cannot convene and vote on the appointment. Even without the confirmation, however, the appointee gets to sit and perform the functions and powers of the position until rejected by the CA or until the next adjournment of Congress.
Regular appointments, on the other hand, fittingly called ‘nominations,’ are made when Congress is in session. The CA is convened to vote on the nomination. Upon confirmation by the CA, it is only then that the appointment is finalized and therefore allowing the appointee to sit and perform the functions and powers of the position.
These illustrate that the President’s power to appoint is not curtailed by the temporary absence of a check and balance mechanism, the Commission on Appointments.
These also present strategic options for the President on when to make the appointments. The choice of “when” spells the big difference.
This was most evident in very recent appointments made by President Benigno Aquino, specifically the appointment of Sixto Brillantes as Chairman of the Commission on Elections. Brillantes was appointed one day before Congress resumed session, a deliberate effort to make his appointment ad interim. This allowed Brillantes to immediately sit and assume Chairmanship without the benefit of a CA confirmation. The president’s desire to appoint Brillantes ad interim was made all the more glaring when the outgoing chairman, Jose Melo, stated that he was asked specifically by the president to advance the date of his announced retirement by one week. This allowed the president a very narrow window of opportunity to appoint Brillantes on an ad interim basis.