Think this might be an Airbus question.
If it is, the answer is for lateral Nav, no - there will be no difference. The FMGC will fly the inbound track of the VOR from the FMGC derived track and you will fly inbound as accurately as if you had pressed the APP button. You can of course fly the vertical profile controlling it with either Vertical Speed or Flight Path Angle selected. What pressing the APP button will do is fly the 3D profile of the approach. The FMAs will annuciate FINAL APP and fly the vertical profile as well.
To do this, the procedure has to be an RNAV overlay approach and the operator has to be cleard to do this type of approach. Not all are.
Last edited by Dan Winterland; 16th May 2012 at 08:43.