1 why should you refactor?

refactoring improves the design of software
refactoring makes software easier to understand
refactoring helps you find bugs
refactoring helps you program faster

2 when should you refactor?

the rule of three
refactor when you add function
refactor when you need to fix a bug
refactor as you do a code review

3 when shouldn't you refactor?

code has to work mostly correctly before you refactor