File -> New Project for ASP.NET MVC projects used to generate controllers with virtual actions. I'm not sure if that stopped with MVC 2 or MVC 3, but is this no longer a best practice?
T4MVC Does make action methods virtual. If you are using it, it should make action methods virtual, no other way it can work
The current documentation for ASP.NET MVC 3 does not show virtual methods. I'm not really sure what making them virtual would gain you, as I've never subclassed controllers to override actions.
If you make them virtual then it will make the controllers easier to mock if you are using them in tests.
Generated code may be made virtual for various reasons. It's not good practice to make your own code virtual unless required by some tool. See Liskov Substitution Principle and Open/Closed Principle. I think some frameworks do this to facilitate creating proxies but I can't imagine any reason to make all of your methods virtual. To me it screams copy/paste or cargo cult programmer.
来源：https://stackoverflow.com/questions/6238068/should-i-make-my-asp-net-mvc-controller-actions-virtual