> then it lacks the greater context of the project

This is the point. I don't want it thinking about my entire project. I want it looking at a very specific problem each time.

But why?

Most code is about patterns, specific code styles and reusing existing libraries. Without context none of that can be applied to the solution.

If you put a programmer in a room and give them a piece of paper with a function and say OPTIMISE THAT! - is it going to be their best work?