As in Smart Client, we can have different layout in Web Client, As Shell form (In Smart Client) used to have different Work Spaces, Here in Web Client we can have different layout representation in Global Master Page. I feel this will be more useful in Web Client, as most of the enterprise web applications have the ability to change the skins, theme also the technology (Lighter version of the website).
 
To achieve something like this, we should have a Layout/Theme Manager which takes care of the construction part that happens in Infrastructure Modules(Say Infrastructure.Layout) after all the modules have contributed the construction information.
 
Refer this link [url:http://www.codeplex.com/websf/Thread/View.aspx?ThreadId=12918&ANCHOR#Post42162]