|"Are you stupid?" - "No!"|
The Balance between the image in each panel and the whole spread of two pages. Mostly it´s a matter of how detailed the work should be.
The Balance between one page and the whole story of 150 pages.
I have sketched out the 150 pages roughly but that is mostly to make sure the story is right planned. To get an idea how long it should be.
The single panel might look good when you only look at it but when you see it together with the other panels it might not work at all.
You need the right balance to get the right flow in the story that you want.