I've seen that in DX11 it's allowed to provide "Fractional Viewports" :
"Direct3D 11 supports fractional viewports; the parameter types are floating-point numbers."
From the docs:
http://msdn.microsoft.com/en-us/library/windows/desktop/ff476260%28v=vs.85%29.aspx
Does someone here know what is the meaning of it? and what potential usage it has?