The JListings Object allows you to configure the Open Graph Object information for Facebook. For instance, you can set the type of all listings in a category to "Real Estate" or "Pictures" or "Products" so that they show differently when a user shares them.
Additionally, by specifically creating an Object for your listings, you have some more control over where the description for the listing is taken from - the intro or the fulltext of the article, along with how long the description should be. That gives you more control than the defaults that JFBConnect would automatically apply.
The "Review" action also goes with a "Listing" object. So, to automatically push new reviews to a user's Timeline for a listing, you will need to the Object configured for those listings. Right now, reviews are the only action we support for Listings.
I hope that helps explain,
Alex