Very important apparently.
Reading it seems simulates the mind. But it doesn't just stimulate the language centers. If you put in scent-laden adjectives, it will activate the scent portion of your brain. Sight, the sight center. Etc.
Metaphors also roused the sensory portions.
Describing actions like "grasped" or "walked" activated the motor portion.
So, like vitamins, it appears to be Good For Your Reader.