My husband has been rebuilding our garage shelving. You could store dead bodies on them. He likes to build things one time and not have to back to fix shoddy work. With the 105 temperatures he was a bit lax on the regular, measure twice – cut once rule.
I'm working with a few clients on new designs and launches of large projects. I'm finding the same rule applies to creative projects. I'd rather have my clients sit with a design for a week and really think about what should change and their needs, modifications, etc. rather than jump on their first reactions, and then redo it several times. Many times we end back to a similar place where we started and sometimes we scrap it and start over.
Whatever the final outcome, having them take the extra time — scratch that — INSISTING they take a few extra days to really sit with it, get feedback from those who should be able to give feedback and then meeting up again saves time for everyone; and frustration. Going over all of the merits of the suggestions, thoroughly may take more meeting time, but saves creative time and produces a much better end product.
Don't forget if the scope or project changes dramatically, don't be put on the spot to come up with a number for the increase in hours and money. Ask them if you can get back to them the next day so that you measure twice – cut once and give an accurate, and realistic quote for all of those involved.