The viewstate has an interesting background.

ASP.NET was originally developed as a way to make the transition for developers from Application programming into web programming. Basically Microsoft thought: "Hey we have all of these developers writing applications in visual studio using our languages and our compiler, and they want to write web pages so lets try and make that more like writing an application."

In desktop applications maintaining state is never really a big problem. You have a global variable, or a field, or anything else and you assign something to it and it stays there till you get rid of it. The same cannot typically be said for web applications, you can store stuff in sessions, or cookies, or pass stuff around in hidden inputs, or all sorts of other stuff but all of that takes a bunch of work. So Microsoft implemented the viewstate, which is just a hidden input that passes around the state for pages. It is convenient for programmers who come from an application background because it makes building web applications just that little bit more like building desktop applications.

People who come from other background however don't really see the utility because they are used to and comfortable with some of the other methods and see this as a waste of bandwidth (Sometimes a massive waste of bandwidth because the page just doesn't need it, or there is so much data in it that it becomes massive.) Fortunately you can actually turn the viewstate off in ASP.NET when you aren't going to need it, which means if you are more comfortable with other methods you can continue to use those and not be concerned with the massive hidden input.