The JT-8 on B732 was indeed one case of needing to know this. It was the norm at LTN, being the BY main base of the ubiquitous B732 squadron, for ATC to give OAT with start up; not the dew point. Over the past 20 years, since I and the world moved on, I've not noticed it anymore in many countries. I wonder if Turbo-props still need this data.