This very simple preference page will be invaluable when you want to make changes to your shop without your customers noticing. For instance, when you are adding several new products at once, or when you want to change the theme and make several tests before making it available to the world.
This page only has two options:
Enable Shop. You can use this option to disable your shop temporarily, for instance when you need to perform maintenance on your shop.
The webservice will still be active, so your data will still be available to those with a key. If you want to also disable the webservice, go to the "Webservice" preference page, in the "Advanced parameters" menu.