Written music or sheet is like a user's guide or manual, it can be a map or schematic diagram or blueprints. Once you are familiar with it then you don't need it. I preferred ear playing. I can read notes, symbols, chords and charts but I am not a sight reader. I can play by ear proficiently. I can identify chords progression even my eyes are closed. I don't trust those fake books sometimes. Some chords are not correctly emphasized. I don't envy those people who can read music but I am more impressed to those who can write notes or music even without using instruments infront of them.