Why pass a wavefunction?

[JonathonMisiewicz]

Psi4 supports users passing in wavefunctions to electronic structure computations. In practice, the user almost always passes a wavefunction as a means to pass in orbitals.

Forte is a Psi4 plugin and therefore also supports passing in wavefunctions to energy calls. Depending on whether the orbitals are orthonormal, Forte may or may not replace the passed in wavefunction with a newly generated one. This strikes me as a possible cause of bugs. If all you know are that the orbitals are orthonormal, is it really safe to assume all the other data on that wavefunction is valid?

In brief, when a user passes in a wavefunction, what information can we safely extract from it, and what can we not? My initial intuition is that we can safely extract the orbitals (after error checking), but everything else is suspect and more reasonably obtained by Forte making its own wavefunction.