There is a thought that both sight-reading and playing by ear are tools along the road towards pure expression. If you think about it, whether you learn music by eye or ear, you are required to formulate music through a series of mental processes until the input (the music you either see or hear) somehow equals the output (what you play). Really, what you are learning is hand and eye or hand and ear coordination. That's not really creating music, except as an after effect. Secretaries use pretty much the same skills when transcribing written and verbal meeting notes. Natural musicians (ie: those who play great with no training at all) rarely play a song the same way twice. Each time, they play what they feel which changes from moment to moment. The only term that encompases this phenomena is talent. Everything done to learn music is in fact a process used to emulate natural talent. So the goal of learning how to play music is actually to grow beyond what you read or hear and advance to a state of total self-expression. Essentially: we learn the rules, we apply the rules, we break the rules. For those with "the gift", there are no rules.