Business value is simply return on investment.
So a developer wants to write module A in some data measurement application because the code looks ugly.
He or she, takes three days to make the module a work of art that passes code review with top score.
Those three days mean in business language
cost_of_moduleA_rewrite = 3 * 8h * salary_per_hour
So that developer just took $cost_of_moduleA_rewrite euros/dollar/yan/whatever out of project budget because the module was "ugly".
So what value does the money spent reflect on the productivity gains of the users, costs related to build software, maintenance costs and so on.
If in the long run it has helped to reduce costs that without the re-write it would be higher than $cost_of_moduleA_rewrite, then it has business value.
If the developer has spent $cost_of_moduleA_rewrite without any positive outcome on project costs, then it doesn't have any business value.
