[kdelok]

Even using the carpentry analogy, I suspect the point is to avoid ruining something on which a lot of time was spent. The material cost of most raw materials isn't very high, but ruining something you've already spent hours crafting is extremely costly.

The other thing to bear in mind is that there is always more work to be done than time to do it. You have to factor in opportunity cost. As many other commenters have said, ultimately it's a balance which depends on your company's particular situation.

[skohan]

> The material cost of most raw materials isn't very high, but ruining something you've already spent hours crafting is extremely costly.

Thanks to version-control software it's also incredibly cheap to experiment freely with an existing code-base in a completely non-destructive fashion. I see no reason to treat existing code as fragile or precious.