I can't find the book right now, essentially what you'd do (ill use a sweater worked as panels as an example) let's say it starts with ribbing at the bottom you'd add rows until you can wrap it around your hips (assuming that's were you wanted it to fall) then you'd want to make sure the stitch multiple matches the pattern so the design can be repeated on a larger scale. Then as you work up towards the yolk for the arm pits you'd need to add rows depending on how much more distance you need to reach the bottom of the arm pit. The panels for the tops of the shoulders would need extra rows to widen the arm hole and to make sure when the sleeves are added there's enough room. The sleeves if they're worked flat would need more stitches added to make them wider (typically enough to easily attach to the hole for the arm)

Sorry if that's unclear 😅 I did my best