The benefits of listing an item with Product Data, is your item has better chances of being surfaced in the search results.
You will need to specify a unique Product Identifier under theProductListingDetails container. You must specify at least one product ID for the listing (ProductID, ProductReferenceID, ISBN, UPC, EAN, BrandMPN, and/or TicketListingDetails). If you specify more than one of these values (such as UPC and BrandMPN), eBay uses the first one that matches a product in eBay's catalog system. (This may be useful if you aren't sure which ID is more likely to result in a match.)
As ProductID and ProductReferenceID are defined by eBay, they provide the most reliable means to identify a product. If you use ISBN, UPC, EAN, BrandMPN, and/or TicketListingDetails, eBay attempts to find a matching product on your behalf and use it in the listing.
You do not need to specify PrimaryCategory with ProductListingDetails, because eBay can determine the category based on the product ID. However, if you specify the category, then PrimaryCategory takes precedence. This means you must make sure that the category is valid for the product ID you specified.
When listing with Product Data you have the following options when listing the item
IncludeStockPhotoURL - If true, indicates that the item listing includes the stock photo. To use an eBay stock photo in an item listing, set IncludeStockPhotoURL to true. If a stock photo is available, it is used at the top of the View Item page and in the Item Specifics section of the listing.
UseStockPhotoURLAsGallery - If true, indicates that the stock photo for an item (if available) is used as the gallery thumbnail. IncludeStockPhotoURL must also be true and Item.PictureDetails.GalleryType must be passed in with a value of Gallery or Gallery Featured.
IncludePrefilledItemInformation - If true, specifies that the listing should include additional information about the product, such as a publisher's description or film credits. If true, Item.Description is optional in item-listing requests.
ReturnSearchResultOnDuplicates - If true and more than one match is found, the call fails and the response returns an error and all matching ProductID values. This lets you choose one of the ProductIDs to pass in instead. If false and more than one match is found, the call fails and the response includes an error but does not return the matching ProductID values.
UseFirstProduct - If more than one product match was found and UseFirstProduct is true, item will be listed with first product information.
ListIfNoProduct - If no product match was found and ListIfNoProduct is true, the item is listed without product information.