The purpose of the guidebox on the Writer’s Portal is to see how users will see your story on their screen, depending on if they read on a phone or on a tablet. The green guidebox shows what tablet readers see, while the red one shows what mobile readers see.
If your speech bubbles are too high or too low, tablet users may not be able to read them. I read Episode stories on my tablet, so for me it’s very frustrating when I can’t read the entire speech bubble. This also happens sometimes with tappable overlays in mini games.
For that reason, I always use the guidebox when coding to see how everything will appear to my readers.
What about everyone else?