AJ was pointing out that there is a need to allow for designs to evolve during the making and being able to take advantage of the sudden inspiration that can strike at any time. I should mention that very few of my projects ever turned out exactly as my original drawings depicted.
There are always things that cannot be seen until they are actually in progress, even if you have the advantage of 3D CAD renderings. Sometimes there is realization that a particular detail will not "read" like it does in the drawings. Something might look good on paper but appear cumbersome when actually built. There is a need to accommodate this and we have to be a bit flexible and light on our feet when it comes to the design.
But that does not mean that you should unilaterally make a change on a job. Especially if you already have approved drawings. The assumption that your client or their designer or architect will see things the same way you do is risky at best and could easily endanger your check! I would never make such a change without first getting approval from the people who are paying for the job! And by approval, I mean signed modifications to the existing drawings that reflect the new idea. It might mean that people have to visit the shop to see what you have in mind. But that is a small price to pay for the assurance that everyone is still "on the same page".
It's one thing to make these changes on a piece you are building "on spec" that will be offered for sale once completed. But on a project that you are building for someone else, it can get you into big trouble and should be avoided at all cost.