We are currently struggling with how to integrate work on refactoring/simplifying/cleaning our product codebase with existing streams of stories and bugs. One of the tricky aspects of this is how to estimate and prioritise the cleanup work: how much is it worth, and how much time should we spend on it this iteration?
Martin Fowler has written about extending the idea of “technical debt” by including the concept of “interest”. Extra time spent on completing any given task compared with the time which would/might have been spent implementing that outcome on a cleaner system is effectively an “interest payment” on the “technical debt”. Noting an estimate of such an amount along with the elapsed time on each piece of work allows a relatively simple calculation of the total “interest payments”, and helps inform any decision to “pay off” the debt by refactoring, simplification, etc.