Beauty is important in engineering terms because software is so complicated.
Complexity makes programs hard to build and potentially hard to use;
beauty is the ultimate defense against complexity.
David Gelernter in Machine Beauty: Elegance and the Heart of Technology
Beauty is an emergent property. You focus on the other stuff (functionality, performance, maintainability, ...) and, when you get that stuff down, you get beauty for free.
William Grosso
Reminds me of this quote from Buckminster Fuller:
When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong.
