Thinking about how your character moves will help you decide how to pose the character when drawing him or her. It will also help you decide how your character gestures, making emotional scenes easier to write becuase you’ll understand how your character would physically react.
Kinesphere: This word describes how “open” your character is, physically. This is often a reflection of their mental state. For example, a character with a wide kinesphere uses broad gestures and may stand with his/her legs apart. Characters on the other end, who have a restricted kinesphere, might be shy. They stand with their hands clasped together, cross their legs when sitting, maybe they sleep in the fetal position.
They could be stiff, like a Vulcan. Thinking about your character’s kinesphere can help you create a more believable character. It can help you decide what gestures your character may use regularly and how they look in their ‘default’ pose. This is a benefit to writers and artists.
For example: A character with a wide kinesphere might reach out to shake someone by the shoulders or slap the other person when they are upset. A character with a restricted kinesphere might clench their fists, stand stiffly, and/or shake with anger, but not reach out.
Want to nerd out? The above information was only a tiny bit of the theory of human movement (Laban Movement Analysis). This stuff is studied by dancers, musicians, physical therapists, and geeks with too much time on their hands. You can join their links by having a look at the Laban wikikpedia entry.