Formerly known as Automatic Placements. When you utilize Advantage+ Placements, Meta will automatically optimize which placements are used and when to get you the most results for your budget.
While advertisers have a long history of manually selecting the placements that they believe are most effective, it is often best practice to turn on Advantage+ Placements. The manual selection of placements may restrict the algorithm and force your ads to be shown in the most competitive placements, driving up your costs.
There are exceptions of course (particularly when optimizing for clicks or ThruPlay), but it usually makes sense to use Advantage+ Placements when optimizing for any type of conversion. The algorithm will optimize in real time based on the performance of each placement to get you the best results.