So far, what I am understanding from these resources is that temporary privileges are commonly granted in the following cases:
disaster relief scenarios
telemedicine and telehealth consultations
any time medical facility has an "urgent need" to deliver "necessary care" to the patient.
A 2010 article from HC-Pro explains "expedited credentialing" vs. granting temporary privileges.
2015 article on pros and cons of temporary privileges. Temporary privileges most common in disaster relief conditions and for telemedicine consultation. The author looks at TJC guidelines and CMS interpretation of guidelines and refers you back to your state hospital organization for direction.