Very simply makes headshot damage do 20 times damage on things that aren't Deathclaws, Mirelurk Queens, Behemoths, Robots that aren't Robobrains, Fog Crawlers, and Hermit Crabs.
If you're doing the quest Diamond City Blues and anyone dies in the opening bar fight, that is a bug, simply deactivate the mod and reactivate the mod before and after the bar fight to avoid it. It's just a small edit to Body Part Data and can be uninstalled or installed freely.