Rewriting from scratch is harder than it looks, but it all depends on how far you existing software is from your goal. Imagine that what you have is a word proc

Rewriting from scratch is harder than it looks, but it all depends on how far you existing software is from your goal. Imagine that what you have is a word processor and you need a web server, surely you would start from scratch. You might say that I chose an absurd example here, but it shows that sometimes what you have is too far from what you need for evolutionary approach.