I'd like to add to this that the Web.Config in the /Views folder is a great (if not thé) way to declare namespaces specifically for your views in. In a web application it is very possible almost every view gets a ViewModel (instead of your actual model) passed to it. Declaring the full namespace after @model or having the same @using App.Web.Viewmodels gets tedious. This way, all viewmodels are automatically available and you have to do extra work to get the real models in scope, which should then set of some alarm bells immediatly.
Also, usually an application can get a lot of extension-methods specifically for use in the view (the HTML-helper jumps into mind). It makes sense to define the namespace to this extension class in the /Views/Web.Config. That way you never wonder "Why cant IntelliSense find my @Html.ImageLink() method??!"
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