Playing by Ear
One thing that doesn't get developed enough for classical musicians or traditional piano lessons is playing by ear. In fact I have known many teachers that actively discourage playing by ear in favor of reading the notes.
If I had to choose between a musician who could read notes and not play by ear or a musician who could play only by ear and not read notes I would always choose the latter.
There are many successful jazz musicians that never learned to read notes. Errol Garner. Dave Brubeck.
Of course the great blind musicians could not read music. Art Tatum, Ray Charles, Stevie Wonder, and Marcus Roberts.