I was early to the digital revolution but was around for a lot of years when film was king. Because of this I have collected a lot of information that has no use in today's photography world. To be a photographer means never stop learning.
I still remember the layers that make up slide, color neg and b&w film. How to process the various types. Ever heard of ortho film? Reticulation? Figuring exposure factors for bellows draw of view cameras (lens to film distance squared over focal light squared gives exposure factor that is converted to the increase in exposure that is needed). When using a view camera do you move the front or rear standard for focusing and why (moving rear standard changes images size). Uses for filters, like 81a, FLD, and 80a. Do you know what filter to use to remove a red line when shooting a document with b&w film (answer is red but do you know why?).
Totally useless information. But that is the beauty of photography. It is a never ending journey. Actually many photographers study other subjects such as architecture or music to obtain a more rounded approach to life, because we do not live in a vacuum. Everything is interrelated and affects who we are and how we interpret what we see.