Try not to reduce things into "good" and "bad" as absolutes - think about the context in which those choices are made, and how they relate to the end result.

As explained in this section from Lesson 1 and in the "path of least resistance" section below it, the goal as far as drawing from your shoulder is concerned for this course is to ensure that when students need to draw with any given pivot - whether the wrist, elbow, or the shoulder - based on the demands of the mark they're making - that they can, without hesitation or consideration to whether or not another pivot is more comfortable for them to use. What we're doing here is entirely unconcerned with how your results for the exercises we assign turn out now - they're exercises because that's where you're expected to be working through the things that are difficult.

Drawing from your wrist is generally something students are entirely comfortable with, given that it's what they've generally been doing thus far, with tons of practice from handwriting. Drawing from your elbow is also not something students struggle with, and tends to get easier naturally as you focus on the shoulder. But drawing from the shoulder is consistently a point of frustration and difficulty for students, which causes them to avoid practicing it.

How you choose which pivot to use outside of this course is up to you - but you'll be in a much better position to make the choices that align with what the specific needs of that stroke are, if you're not in a position to specifically and actively avoid using one of those pivots.

I maybe be wrong but the reasson why we should use the arm in every situation is not because is better but for make our draws with the arm better. When more we use the arm to draw better will our lines with him