In my previous post, I talked about how your bone is not merely structural, but is also a mineral store for you body. It turns out that muscle is not merely for generating force, or for impressing other people, but is the protein store for you body.
Why should you care? If your body suffers some kind of damage, it will need to repair itself. It will use protein to do so. Where will it get it? From food, or, if there isn't enough dietary protein, from muscle. See this article for details. Burn victims and cancer survivors do better with more protein stores, for example.
It turns out that muscle doesn't just protect you from injury by making you stronger, it provides a necessary reservoir of amino acids to help you get better after injury or illness. As Mark Rippetoe has famously said, strong people are harder to kill, a fact that the medical literature supports.