It's worth knowing when it's useful to apply. Needlessly duplicating code also creates another kind of complexity: large surface areas of change that need to be

It's worth knowing when it's useful to apply. Needlessly duplicating code also creates another kind of complexity: large surface areas of change that need to be updated in tandem. If you get changes where you have to change multiple places at once in the same way it's a good sign you need to do some refactoring before someone accidentally introduces an error into the program.