How does the iOS restriction "Force limited ad tracking" work?
Apple outlines the functionality of limited ad tracking here. Essentially, users that have this option enabled can expect to experience a lower amount of targeted ads when using applications and browsing the internet. Note that this does not eliminate ads altogether, they just won't be specifically targeted to a user based on usage habits. When using a particular application or viewing a particular website, the ads may still be related to the content of the application or website itself, but wouldn't be related to any external usage factors.