In most cases, you should use an implicit saving model when users create or change data and then leave the screen (for example, navigate to the previous screen). In this model, data is saved automatically without requiring users to perform a Save action. For example, you can implicitly save data when users change one or more options or change the details for a contact. This approach allows users to get things done without having to pause and be interrupted.
In rare cases, you can use an explicit saving model. This model interrupts users and requires them to indicate whether they want to save or delete data. You can use this approach if it would be very time consuming for users to recreate the changes (for example, when users set up a Wi-Fi connection, type an email message, create a meeting invitation, or edit an image or video).