What's the purpose of nutmeg in mashed potatoes and white sauce? I've seen lots of recipes that call for a pinch of nutmeg in mashed potatoes and in white sauce.  It's not very much and just provides a slight elusive flavour.  I do enjoy it, but often don't bother with it and I'm just wondering what the purpose of it is?  

Is it just a tradition, or does it actually serve some specific purpose?

Is it a little like the ubiquitous teaspoon of vanilla in baking, which is ostensibly to promote other flavours and you usually don't really taste it in the final item?
I think you've answered your own question. It adds an elusive flavor that most people feel enhances the creamy flavors.