You can get a sense of the difference between the two profiles by comparing screen-shots of the Visual Studio IDE layout immediately after the two different “Web Development” profiles are applied:

Screenshot of the "Web Development" Profile

The layout below demonstrates the default IDE layout (at a 750x650 monitor resolution) when the standard “Web Development” profile is applied.  This profile is an evolution of the existing “Web Development” profile in VS 2008 and exposes design/split/source tabs within the document window of any HTML or ASP.NET page:

Screenshot of the "Web Development (Code Optimized)" Profile

The screen-shot below demonstrates the default IDE layout (at a 750x650 monitor resolution) when the new "Web Development (Code Optimized)" profile is applied.  As you can see, the profile optimizes the screen real estate around displaying and editing code on the screen, hides all toolbars by default, and disables and hides the designer tabs within the document windows of HTML and ASP.NET pages:

Below is a screen-shot of the “code optimized” profile at a larger monitor resolution: