When you are editing your images or working on your designs and are using the brush tool in Photoshop (available by pressing the B key, or via the Tools menu (Image A)), changing the Brush attributes (Size, Hardness and Opacity) on the tool panel (Image B) can reduce your performance and get in the way of your working.
You are able to work much faster by changing the size, opacity and hardness of the brush while you are editing. This option is available when you are in in the brush tool and if you are using a mouse or a tablet (i.e. Wacom tablet). Holding down the CTRL+ALT keys (if you are using a mouse, you will also need to hold down the Right mouse button), however a Wacom tablet (like the Intuos 5) works great with no additional actions. When this keyboard shortcut is used with a movement of the mouse or a Wacom pen a heads up brush with configuration attributes will be displayed. By default Photoshop is configured to change the brush diameter when moved from left to right, and moving up and down will change the hardness (see below), the red colour will reflect the brush configuration and the attributes are show within the black box.
Changing the “Vary Round Brush Hardness Based on the HUD vertical Movement” setting on the Photoshop preferences panel under the general tab will allow the Hardness configuration to be changed to control the Opacity of the Brush
The brush settings in Photoshop CS6 are always shown using the Black heads up display when using this feature.
On a side note, this information is powered by the Graphics Processor on the computer you are using, so should not have an impact on the performance of Photoshop CS6.