I can delete Html.HiddenFor(model=>model.Id) and the app still works. What is it for? - asp.net-mvc

Question

If VS creates a strongly-typed view for the [HttpGet] Create, I get markup for the model as follows.
Note that the code has been simplified for the sake of brevity. The important point is that VS does NOT include Html.HiddenFor(model=>model.Id).
//Create.cshtml
#model MvcMovie.Models.Movie
#using (Html.BeginForm())
{
#Html.ValidationSummary(true)
<fieldset>
<legend>Movie</legend>
<div class="editor-label">
#Html.LabelFor(model => model.Title)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.Title)
#Html.ValidationMessageFor(model => model.Title)
</div>
<div class="editor-label">
#Html.LabelFor(model => model.ReleaseDate)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.ReleaseDate)
#Html.ValidationMessageFor(model => model.ReleaseDate)
</div>
<p>
<input type="submit" value="Create" />
</p>
</fieldset>
}
Now I create a templated HTML helper EDITOR named Movie.cshtml for the type Movie as follows.
Note that the code has been simplified for the sake of brevity. The important point is that VS DOES include Html.HiddenFor(model=>model.Id).
//Movie.cshtml
#model MvcMovie.Models.Movie
#Html.HiddenFor(model => model.Id)
<div class="editor-label">
#Html.LabelFor(model => model.Title)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.Title)
#Html.ValidationMessageFor(model => model.Title)
</div>
<div class="editor-label">
#Html.LabelFor(model => model.ReleaseDate)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.ReleaseDate)
#Html.ValidationMessageFor(model => model.ReleaseDate)
</div>
If I use this templated, I must change Create.cshtml as follows:
//Create.cshtml
#model MvcMovie.Models.Movie
#using (Html.BeginForm())
{
#Html.ValidationSummary(true)
<fieldset>
<legend>Movie</legend>
#Html.EditorForModel()
<p>
<input type="submit" value="Create" />
</p>
</fieldset>
}
The questions are:
Since the hidden field form can be deleted without any side effect, in this case, what is the hidden field for?

Answer 1

It adds hidden field because it doesn't know how action looks like. Action will contain parameter ID in url thus it is not required to put it into hidden field. However in template, VS doesn't know whether action will contain ID or not, so it puts there hidden field holding id to be sure.