Since AutoCAD 2011 the Quick Access Toolbar became more flexible. By default it delivers the Workspace Switching but might be a better idea to have your Layer Control instead. You might be in your Annotate Tab and need to change the layer. Then you have to go back to your Home tab and the back to Your Annotate Tab AGAIN. It just makes it easier and faster to access from your Quick Access Toolbar. You would have to add the layer control box to your Quick Access Toolbar trough your CUI (CustomizeUser Interface)
You can find your CUI in the manage tab and Customized User Interface or just type in the word CUI In your CUI locate to your Quick Access Toolbar Tab
At the bottom drop down choose Ribbon Control Elements:
In the bottom list choose Layer List Combo Box and drag and drop that underneath your Quick Access Toolbar at the top.
Apply and OK, and your Layer dropdown list will appear in the Quick Access Toolbar.
Please follow this link for the video: http://youtu.be/BgCMNn7OjjM