As a developer, you have to take into account future modifications to requirements. As a game developer, this is not really different, but there are layers to that 'taking into account'. 

While at first you have the feeling you have everything ready: The game play, the structure of the levels, the story development. You will easily find out that because the game play changes, the levels don't work in the size you envisioned them and even the story doesn't run in the same direction anymore (or you want to add something to the story. 

For Visual Novels this is even more apparent, as story is the main level of structure....but when you are creating illustration to your narrative, you will find out that sometimes a new image either doesn't fit with the story, or shows you that some part of the story could be more deepened...or extended. You have to be weary of this.

Another thing is, that as you learn to create visuals, or code for a Visual Novel (whichever engine you use), you will find out that there are additional parts to take into account.

I for one, thought I could create images in DAZ, without requiring much post processing. How wrong I was. Now there is an additional step to work through the images...and this means there is also a requirement to re-render some images.

Not a big problem, just more time required. Luckily I am only a limited amount of renders into the game. Image you are like hundreds of renders on and then find out whole scenes have to be re-rendered....ugh...