To avoid any potential drops in performance, Google recommends setting a similar budget for your Performance Max campaign as any existing Smart Shopping campaigns. This is to ensure that your Performance Max campaigns can capture previous shopping inventory.
If you’re still running Smart Shopping campaigns, then it’s recommended to stop them completely and allow Performance Max to take over and allow the machine learning algorithm to begin collecting data. It may take two to three days for your new Performance Max campaigns to fully take over your Smart Shopping campaign inventory.
As with any advertising campaign, looking at reporting and data is crucial. While Performance Max doesn’t give retailers access to all data, it does show you some actionable insights on how the automation is working. You can view consumer interest insights, audience insights, and search trends. This will be leveraged automatically by Google's AI learning process to better optimise campaign performance.
Be aware that Performance Max campaigns will be prioritised by Google over Smart Shopping campaigns that run the same products in the same account. This will cause spending in your Smart Shopping campaigns to significantly decrease, and Performance Max will increase in its place.