Jeff Veen at @media showed a nice graph, and Indi Young used it afterwards. But I don’t have a copy of it, so I’ve recreated it below. I think it shows really nicely the benefit of discussions early on, and the impact of a change of mind later on.
It’s great: At the start, you can have whatever you like. Near the end, even if you change the tiniest little thing, it has an impact.
The aim of the graph is to encourage talking and interaction at the beginning, not scare people about cost.