When turned on, Meta can expand your audience to reach people beyond the Detailed Targeting (interests and behaviors) that you selected, but only if that expansion is expected to lead to better results. Location, age, gender, and exclusions are hard constraints, and the expanded audience will continue to follow those rules.
Advantage Detailed Targeting is on by default for most objectives and cannot be turned off when optimizing for conversions or app events.
Read more here:
Advantage Targeting: How Meta Audience Expansion Products Work
