In a Shopping campaign, conversion tracking:
only counts purchases after clicks as conversions
grants access to Search Funnel reports, which show how your customers complete a conversion
provides in-depth reporting on how people use your website
allows you to test changes, such as different campaign priorities and product group bids
Once you’ve set up conversion tracking, you’ll have access to a handy set of reports about your conversions.
Attribution reports show you the paths customers take to complete a conversion, and attribute the conversion to different ads, clicks, and factors along the way.
Read more here: https://support.google.com/adwords/answer/1722023