I'll agree that they are often a very bad idea. But there are advantaages: 1) Writing the same code a second time often results in cleaner, more efficient co

I'll agree that they are often a very bad idea. But there are advantaages: 1) Writing the same code a second time often results in cleaner, more efficient code that is easier to maintain. If you don't believe this, write a small app. Then start from scratch and write the same app again, from scratch, without looking at the other. For further proof, do it again. 2) Some code is just not maintainable. If you can't test it, you can't change it without fear of breaking something. I usually do my best to write tests for the old code, but sometimes that's just not possible. 3) Feature creep. That old code was designed to solve an old problem, and then modified many times to solve newer problems. There are a ton of features and quirks that aren't useful any more, but nobody removed them. If you tell a PHB "I'm going to remove a feature" they will freak out. If you tell them, "That feature didn't make it into the rewrite because it's not used enough" they will thank you for saving the company money. (Bosses that get it are different, but this tactic is still more palatable.)