Add to cart pop-ups can collect opt-ins when someone presses the add to cart button on product pages.
When to use an add to cart pop-up
An add to cart pop-up is great when you want to capture opt-ins from people at the point of adding an item to the cart.
Even if the customer doesn't opt-in, their items will still be added so this can be an effective time to offer a discount.
Advanced (optional) behavior settings
This setting is useful if enabling an add to cart pop-up causes behavior with the add to cart button that isn't expected.