They are also used when getting measurements from other parts of the pattern. If you use a standard (multisize) measurement file, these will be dynamic when changing the size of the pattern, so your line will always be the length of the curve, no matter what size of the pattern you choose. But is you are using an individual measurement, you can also use the formulas. If you change the pattern, it will change ell the formulas used automatically. So using formulas is always a better way than entering fixed numbers.
Sorry, I've just translated this bit and yes, it's exactly as you say