1. In some cases(your examples) they are definitely added afterwards to emphasize the thinking/strategy behind the design but to add them afterwords you need to use them as you construct your design, then when your done, maybe half if not all of them are gone, but you can re add them and do the same as in those examples in order to illustrate the thinking behind the design.
2. Sometimes, they actually are part of the design(final piece) not just the one for presentation/showcase version.
3. Ah, and the final case, I do not recommend this, but sometimes they were not even used when constructing the design, but added afterwards(not so complex as in your examples) just to convey that look of carefully thought design... I've seen architecture students doing it, cause the teacher was always obsessed with them to calculate and measure everything they draw, so they would draw freehand and at the end they would add such lines to make it look like it was all measured and calculated. For example at the edges of a cube, they would make the lines of the cube a bit longer longer than the faces at the end(like in the picture bellow)..it just gives that effect that there is some kind of thought/professional technique behind the drawing/design.
It just adds more value to your design and can help the viewers undersand it(if thats your goal). Look at the screenshot bellow, when you first see the eye shaped Fill Shape it looks kind of dull and booring, but if you look at the other image bellow it, you can see how it was constructed, you just understand it better, it helps, sometimes...