1. Cross-Site Tracking
Cross-site tracking allows apps and advertisers to track your movements and behaviors across other websites — so even when you aren’t on that specific app, it can still track you. The advertiser or app will embed trackers (cookies and scripts) on that site and then follow you and take little snapshots of your actions, particularly if they involve shopping for products and making purchases. Even the act of showing interest in a product is enough to get these trackers excited, and it’s why you will then return to an app like Facebook and see several ads for that exact product or similar ones.
To get this under control, go to Settings > Privacy > Tracking and toggle off "Allow Apps to Request to Track.”
2. Location Services
When Location Services is turned on for your apps, they will be able to see your physical location as you travel throughout your day. This information is crucial to them as they can better learn your habits and needs and target ads to you based on those needs. Knowing your location also makes it easy for the app to provide geographical information about photos that you post.
Some apps require your location to work properly — think of navigation apps, weather apps, and apps that deliver food to your door. But the vast majority of them do not need to know your whereabouts, and you never have to allow an app to access your location when you aren’t actively using it. Go to Settings > Privacy > Location Services. Turn off Location Services completely or change your permissions for each individual app.
3. iPhone Analytics
Apps rely on iPhone Analytics to gather data about its users, including how they interact with their apps. On the surface, this can be a positive thing: an app developer can rely on this data to fix bugs, improve user experience, and create better features. But you aren’t beholden to app developers to help them improve their product.
To disable App Analytics, go to Settings > Privacy > Analytics & Improvements > turn off the toggle for Share With App Developers.