NO ONE IS PROMISED TOMORROW!
With that said, yes, your chain of command cannot force you to get a will or power of attorney but it is smart for every service member to do so.
You do not know if anything might happen to you during your travels or training that will leave you dead, injured or mentally incapacitated.
I been with the Mrs. for a very long time and I give her a general or special (which is more specific) power of attorney and not only when I am deployed or on exercises. She secures the notarized document in a secure lock-box.
If you have a significant other or a close relative that you trust with your finances; then it behooves you to get one. It is smart sense.