I've asked the same question, and in my case, it matters only somewhat. For those who have 'temporary' PN -- like from a vitamin deficiency or a few other causes -- it indeed matters because finding the cause suggests the cure. For those whose PN is progressing rapidly it also matters because they are racing time.

I gave up on finding the cause of mine because it didn't seem to matter, except that I discovered some triggers that exacerbate it and the RLA that stopped the burning. Even though I repeatedly test negative for any kind of diabetes, my PN reacts as if I were diabetic, so I listen to my body.

Once again, it seems to come down to everyone being different, though I tend to agree that there may be a fair percentage of people for whom the cause may not matter -- only the symptoms can be treated. YMMV.

Doc