You can use campaign priority to:

You can use campaign priority to:

• A) Speed up how fast a campaign’s budget is spent throughout the day
• B) Have Google prefer certain inventory in query matching and ad serving
• C) Tell Google which campaign’s bid to use for a product when the same product is included in multiple campaigns
• D) Make your Product Listing Ads more competitive in the auction

Explanation: When you have the same product in multiple Shopping campaigns, you can determine which campaign should participate in the auction for that product with campaign priority. Your campaigns already have a priority: Low. But you can change this priority to Medium or High. These priorities determine the bid for any product that the campaigns share.

Read more here: https://support.google.com/adwords/answer/6275296?hl=en