MMPI-3 Not as Clinically Useful as the MMPI-2
The MMPI-3 is not an improved MMPI-2, but only the next step in the MMPI-2-RF. You will not see much on it being more valid than the MMPI-2, because it is not. The RF and the MMPI-3 should have been additional content scales to the MMPI-2, but there is no money in that. The RF and MMPI-3 are good self-report scales of obvious item content, and do have some usefulness in situations where the person is motivated to self-disclose. However, the MMPI-2 is more subtle and more clinically sensitive (Gordon, R.M., Stoffey, R.W. & Perkins, B.L. (2013) Comparing the Sensitivity of the MMPI-2 Clinical Scales and the MMPI-RC Scales to Clients Rated as Psychotic, Borderline or Neurotic on the Psychodiagnostic Chart, Psychology: Special issue on Criminal Investigative Psychology, 4, 9A, 12-16. doi: 10.4236/psych.2013.49A1003).
I have seen some practitioners give both tests. I do not understand why. If you give the MMPI-2, you do not need to also give the MMPI-2-RF or MMPI-3.