In a reply to my last post, it was suggested that "a preliminary, or more formally, presentation drawing can be a real problem solver …" and this is unarguable. Improvising is not something you do on someone else's nickel.
It's one thing to "make it up on the fly" when you are experimenting or doing a project for yourself and are unsure of the exact path you want to take. A fail in this situation may not be the disaster it would be if it happened on a client's project.
I have rarely done a project without some preliminary planning, including detailed drawings or at least some sketches to serve as a guide. But I have never done a project for a paying customer without a set of fully detailed and dimensioned working drawings. In these situations, there might be a "TBD" (to be decided) on some detail or another but these are usually minor.
Having said that, the point I was trying to make is that even detailed drawings are not always revealing of every possible eventuality. It is quite possible to draw something that is impossible to build. One need only look at the "devil's fork" or the drawings of M.C Escher. So we still need to be prepared for those moments when we realize that our plans need some additional work. We can only hope that that additional work does not end up eating all the profit!