It's the "Chest" slider, Cece. It won't break your game by any means (slider borked-ness is largely only a visual problem) and you can certainly keep it, but just keep in mind that if you use it at an extreme it seriously distorts the sim's head - almost into like, a crescent shape from side view. Some people called it a "waning" and "waxing" moon effect. I ended up taking it out, just because I didn't want generated townies rolling an extreme value on the slider.