Always, but with regards to writing clean code, it pays to just learn how to do this upfront. An analogy is of cooking. I used to be a very messy cook, the food is just as good, but when I was done the kitchen looked like a bomb had hit it. Cleaning becomes intimidating at that point. Learning to be cleaner in my processes didn't change the end result for the food, but made the rest of the evening much more pleasant. Professional cooks and chefs learn to optimize this, they are neat and clean where this is most efficient, and offload cleanup to a plongeur where necessary.

Secondly I believe that with practice, DRY can become second nature. Back in the mid 90s I wrote a lot of COM code in straight C (for reasons). This ends up being extremely verbose, so repetition carried a sufficient penalty that I learned to avoid it, to carry a sufficient mental model of the code base to know when I could avoid repetition.

[edit] plonjeur -> plongeur