What does Layout=null and ignoring the Layout property within the View means ?
This is pretty simple , Layout=null , the view does not use any layout and the layout of the page will be the one used within the view.
Ignoring the Layout property is a different story . Sometimes , ViewStart file can be used with the Views folder to define the layout for each view .
In this case , when the Layout property is ignored in each view , the ASP.NET MVC will start finding the layout mapping from the View Start file.