Targeting Expansion in Amazon Ads allows the platform's machine learning to automatically broaden your campaign's reach beyond your explicit targeting, by identifying and showing your ads on other closely related products or searches that shoppers are engaging with.
You should generally enable this feature when you're looking to discover new growth opportunities, increase impressions and reach to a relevant audience, or leverage Amazon's automation to find new high-potential targets without constant manual effort.
However, exercise caution or consider disabling it if your campaign demands extremely precise control over ad placements, or if your ACoS (Advertising Cost of Sale) or ROAS (Return on Ad Spend) is already very tight and cannot absorb any temporary fluctuations as the system explores new, albeit related, placements.
