Basic Server Control / Control Returns The [id] Or The Text That Is Set?

I'm looking at server controls for the first time, and I've a question about this code:

[Bindable(true)]
[Category("Appearance")]
[DefaultValue("")]
[Localizable(true)]
public string Text
{
get
{
String s = (String)ViewState["Text"];
return ((s == null) ? "[" + this.ID + "]" : s);
}
set
{
ViewState["Text"] = value;
}
}

I do not understand why this control returns the [id] or the text that is set. I do not see how this makes any sense. Is this just for demonstration or is there a reason for returning the id?