Because you might need it one day
First the disclaimer. Yes, there are a lot of problems with using session in your ASP.NET applications. Moreover, by default, HTTP (and by extension, REST) is stateless – and as a result each HTTP request should carry enough information by itself for its recipient to process it to be in complete harmony with the stateless nature of HTTP.
So if you are designing a proper API, if you are a REST purist, or if you are Darrel Miller, you definitely do not want to continue reading this article. But if not, and you find yourself in a scenario requiring session – perhaps you are using Web API to facilitate your JS or MVC application, and you want to sync the state of Web API with the state of MVC easily, or you simply want a quick and easy way to persist state on the server side – this article is for you.
More after the jump.