When deciding whether to duplicate a Facebook campaign or an ad set, it is important to consider your specific goals. Duplicating a campaign is often useful when you want to replicate a successful campaign with multiple ad groups, testing different variations within the same campaign. Duplicating an ad group, on the other hand, is appropriate when you only need to adjust specific elements like the target audience or budget, without changing the entire structure of the campaign. This decision depends on whether you want to maintain consistency across the entire campaign or focus on optimizing individual ad groups.