When you have the same product(s) in multiple Shopping campaigns, you can determine which campaign should be prioritized for those product(s) with campaign priority.
The three Campaign priority levels are:
Low: Best suited for catch-all campaigns. Google/Bing will serve these product ads last before any other priority level.
Medium: Best suited for Primary or general use campaigns. Google/Bing will serve these products before Low priority campaigns, but only when Medium priority campaigns have enough budget.
High: Best suited for hyper-targeted campaigns such as Top Performers or Mobile Only. Google/Bing will serve these products before Medium priority campaigns, but only when High priority campaigns have enough budget.
Use Case Example
You have a general campaign with all products running at a Medium priority. After a few months of activity you're finding that there are 20 products that are always top performing in conversions and ROAS.
You create a Top Performers campaign, adding only these 20 products to it. You keep those products in the Medium priority campaign as well.
By setting your Top Performers campaign to a High priority, you are telling Google/Bing to serve those 20 products in it first. Should it run out of budget, the Medium priority campaign would then be next to serve those products.