SOPP666: Can you please clarify when using a thumb on black notes is or is not proper fingering”

Secrets of Organ Playing Podcast

This question was sent by Bob, and he writes:
“I have read in several places that using the thumb on the black notes is kind of frowned upon. The "Organ Playing Master Course" routinely calls for the thumb on a black note, can you please clarify when it is or is not proper fingering.”