What is it about bit-rot that seems to drive us away from quality? Here's the analogy:
Let's say you just bought this massive steak that you're going prep before the game. So you know you're gonna create an awesome rub then toss it on the grill at a solid 600° and just go to town on the beautiful cow bouquet.
You get to the counter and it is covered in the remains of last night's game fest. Baring any cultures that the CDC might want to take for posterity do you really stop and think... "Hmmmmm, should I clean the counter before I do the rub throw-down on this $50 steak?" No you don't... so why do we do it with the code we write?
You're in some pretty rough code and you add a beautiful bit of code to it, do you leave the other bits around it trashed; lipstick on a pig. Word to the wise, be a boy scout, leave it in a better condition than you found it.