Only if you place a high priority on thickness. I personally don't, and am actually fairly annoyed that cell phone makers don't have the option to e.g. double the thickness of their phones in exchange for a 2-3x increase in battery life.
They have this, it is called a Mophie Juice Pack[1]. They have two sizes with different battery extensions.
I miss the thinness of my phone without the case but greatly prefer being able to get through a day in the data center or traveling without constantly charging my phone.
Of course. My point is only that people don't all have the same priorities. If you strongly value thickness, a case is not a good choice. If you don't care, then a case is a good choice. Making a blanket declaration that a case is "pretty costly as far as insurance goes" regardless of personal preferences is stupid.