The XMP file contains your edits. Yes it is essential, if you delete it you will lose your edits if I understand your workflow (although in other workflows it is not essential, but some people like to have it there anyway).
A better approach is to not export the file, but to leave the photo in Lightroom, and if you need to continue editing the photo, just go to the Library module, select the photo, and then go to the Develop Module. This will display your original edits and then allow you to make further edits. In this fashion, no XMP file is generated (although you could optionally create one, some people like to do that).
Thanks so much for your response The (probably basic!) issue I'm havig it that I just want to get my photos from my camera to Mac and file them. I dont want to go though Iphoto, so chose to use lightroom and therefore finding the extra XMP file.
Is there another way to get RAW files to save on my computer direct from my camera without using Iphoto etc or creating an XMP file (all pre edit, just a save initially)?
It never did this on version 4 or on my PC.
This is probably a really basic question sorry! But after moving from PC to MAC there's definatly a few things to get used to.
Many thanks in advance
This is not a Mac vs Windows issue, it most likely is an option has been turned on (accidentally?) in Lightroom.
You could use Lightroom, making sure that the option to write metadata to XMP is not checked (see Adobe Photoshop Lightroom 4 * About metadata and XMP)
An alternative method: You could simply use your operating system to copy the photo from camera card to whatever folder you want it to be in.