The Washington Post explains one way that Khalil Mack can help the Bears defense:
"Adding a fearsome pass rusher like Mack could turn Chicago’s fortunes around in a hurry. According to data from TruMedia, teams scored almost two points per drive in 2017 when the offensive line didn’t give up a sack. That dropped to less than a point per drive when yielding one sack or more, making it easy to see how much of a momentum killer a sack can be. And with Mack, the Bears should be getting plenty more of them."
Full article: The Washington Post