As the name implies, the tip of the pen on the side where strokes are written depends on the specific structure of the side-looking characters, which is more common in running script. The strokes on the profile strokes give people a sense of movement, and when the writing speed is fast, there will be flying white; In the running script, there will be many combinations of center and winger. Different calligraphers have their own understanding of the proportion of their use, which requires long-term accumulation to form their own calligraphy style. For example, Mi Fei, a great calligrapher, claimed that his calligraphy was a "brush character", which actually showed that his calligraphy style was versatile.
In short, the center and the side are just one stroke, and each has its own function. Rational use can reflect the beauty of calligraphy. That's all.