It is an absolute requirement if you want to build something that (1) uses a classifier as part of a larger system, (2) can be let off the leash with no human supervision and (3) is not an AI slop demo that will be [dead] and [flagged] in seconds after being posted to HN.

For instance if you have a predictive model for market prices that is not calibrated that's... nice. If you have a calibrated model you can add a Kelly better and you have a trading strategy that makes money. Similarly if you are classifying articles or images or other contents to make a feed you might believe that 70% or 95% or some other level of precision is "good enough" and you can set the knob and turn on the cruise control.