[paulhauggis]

Sometimes, it's just not a good idea. If you have a piece of software that has been battle tested and many of the bugs have been worked out over the course of several years, you will have an entire new set of bugs with a complete re-write (which could take lots of time to figure out).

I've also seen this as a solution to many problems because it was much easier for the developer to start over than to figure out the existing code and try to work with it.

But, there are some instances when a rewrite is the answer.