- Edited
An additional difference that sometimes seem to get lost in the discussion is that while a performer has good reasons to practice every piece until it is 100% solid, this is probably not the most efficient use of time for a student whose larger goal is to improve on the instrument. After reaching 90-95 % "perfection" the additional effort to get the piece close to 100% is not at all proportional to the relative improvement. I often think in terms of the pareto principle. The exact numbers quoted vary, but the general gist in this context would be that we spend maybe 20% of the time to get 80% of the desired result. The more we keep polishing the more diminishing returns we get for our effort and time. Personally, my impression is that I learn more per time unit in the early stages and I'd generally rather play 5 pieces to an 80% level than one to 100% if my goal is to learn the instrument or explore music. This of course doesn't exclude polishing some pieces to a performance level, but quantity based approached like 40 pieces a year etc certainly have their merits. One quote you often hear is "Students practice until they get it right, professionals until they can't get it wrong." with the underlying assumption that the professional way is the right way, while in fact the student might actually be doing what is long term optimal for where they are.