Submitting a sitemap XML file to Google has the advantage of achieving more structured results when Google crawls your store's pages and publishes their content in search results.
Submitting the sitemap XML file is not a requisite to getting your store's content listed on Google.
The process of submitting it to Google's Webmaster Tools merely expedites that process and provides Google's crawlers a more structured way of knowing where to look for your content.
A Google Webmaster Tools account also provide you with information about your website's indexing and rankings.
It is completely optional!
Please note that Google will index all of your pages irrespective of whether you submit the XML file or not.
All of SupaDupa's boutiques make it very easy for Google to do so and it is a key objective for us to ensure that our member's pages rank well in search results.
You can find your sitemap XML file by typing in your store's URL followed by 'sitemap.xml'
To sign up for Google Webmaster tools where you can submit your sitemap, go to:
http://www.google.com/webmasters/tools/
For an annotated screenshot which highlights the steps to carry out on the Google Webmaster Tools website:
http://monosnap.com/image/V2X7drfJ9xd1lmWDM2LSmbyGU6DSGC
Additional Info:
http://support.google.com/webmasters/bin/answer.py?hl=en&answer=183669