A Diagnostic Wax-up is a great way to get visual reference for the patient and something that they can see and hold for themselves, seeing the difference of before and after.  From the wax-up the Dentist can quickly make a temporary for the patient so they can try-out their new smile.  This gives them time to go home and see if this new smile fits them.  From this point the temporary can be modified until the patient is completely satisfied.  This helps ensure that on the delivery day of the final restorations everything goes smoothly, since the patient knows exactly what to expect.