This "bad" habit has some legit mind / body benefits says recent research:
IT REDUCES STRESS
The repetitive action can be calming, says Andy Smith, PhD at the UK's Cardiff University.
IT SHARPENS FOCUS
"This maybe because chewing ups blood flow to the brain," Smith notes.
IT CURBS CRAVING
People who chewed gum in a Louisiana State University study had fewer food longings and ate fewer high-calorie sweets than their gum-free peers. Gum may trick your brain into thinking it's already had a sweet food, giving you a feeling of satiety, researchers say.
Source: Health.Com Magazine, October 2012 Issue