The Adjustment Brush in Camera Raw has a few settings that can change the way you brush. For example, there's a Size setting which is pretty obvious. There's also a Feather setting which softens the edges of your brush. And finally there's a Flow setting that affects how much of the effect is applied in each brush stroke. Well folks, right below that is a Density setting and we've gotten more questions about this little setting then anything. Wanna know why? Because when people try adjusting it nothing really happens. That's because the Flow setting really does it all and Density barely does anything. So stay clear of the Density setting. Leave it at 100 and be done with it. If you want to adjust the characteristics of your brush then go with the other 3 settings.