The perennial question.
Well, when I started out, I always printed full frame (eg 8x12 from 35 mm neg) because I didn't want to waste anything, I could never understand why people printed 8x10, 11x14, etc.
Now I realise that cropping is an essential part of the output process, and that it's not a single-answer problem, ie the answer is not always "print full frame".
Cropping serves many purposes, one of the most important is to support what you are trying to communicate with your picture. You crop elements which distract, which don't add to what you're trying to say, etc.
For a square neg, we have another decision. A picture cropped and presented vertically can have a different feel from one horizontally. Unlike 35 mm photographers, we can leave that decision to the output stage.
Hence my answer is-- I'll print full frame if that works, I'll crop if it works better. To me, printing full frame is not a sacred cow.