As an amateur web designer I've been paying close attention to websites' designs to improve my grasp on this field, I noticed that some websites are using sticky navigation bars while others are using non-sticky ones (such as SE). So, I've been wondering, why are they choosing one option instead of another?
What are the basis of choosing a sticky navigation bar anyway? Is it the page's length(longer pages need a "return point")? Or perhaps it's based on application's type (web apps need sticky navbars to look more app-y)? Or maybe it's just designer's personal preference?
P.S.: I've seen websites using both sticky navbars and non-sticky ones, such as SE chain and Twitter.com, and indeed both of them are well-made. So I really don't think there's a bad design choice here.