I've noticed that when I sketch using wrist movement I often get inconsistent line shades and widths. Recently I tried locking my wrist and only moving my arm. What I saw was a mix of good and bad results. I was able to get extremely smooth line widths and shades, but I found it difficult to apply to subtle areas. I've seen a few professional animators draw on video, and they all seem to almost entirely rely on arm movement when drawing. I was wondering if I should continue to practice drawing this way, or to go back with bending my wrist and just trying to be more careful when drawing that way? In the long run drawing with my arm saves lots of time because I'm usually able to get draw one side of someone's body in one stroke, and then I just make minor corrections after getting the general outline.
Any input on this technique would be really appreciated!