Technical Debt Overuse of Global State You wouldn't control the water temperature in your entire house from a single location. Why would you write your code that way?
Technical Debt Old Fields Left in Place Leaving old fields in place is even worse than leaving old code. Instead of runtime errors, you'll end up with harder-to-detect data errors.
Technical Debt Old Code Left in Place What's the harm in leaving old code in place? It's not like it costs us anything. ... Or does it?