From the recent update of iOS 7 in iPhone, there is a feature added that can be used to track people. It is a feature that was incorporated in the compass app. The feature includes a Frequent Locations services. What will happen is Apple will collect the GPS coordinates obtained from the Frequent Locations shared from your iPhone to improve its Maps.
The information is also used by Apple to improve the Geographical location from the resulting coordinates of your iPhone to for the improvement of Apple Maps.The GPS technology that is embedded in the iPhone that helps you to navigate yourself to places is now also being used to provide data to Apple. However Apple does claim it collects the data based on anonymity.
The problem with this is by giving your Frequent Locations to Apple, it is considered intrusive and also they will know where are your favorite hangouts or the usual place that you use to go. This data is very valuable to some companies and advertisers. They can collect the data and analyze the trend and also your lifestyle.
It is interesting also that if the Government wants to keep track on some people and requested Apple to provide that information, will Apple provide the data? However you can choose to turn this off by going to Settings –> Privacy –> Location Services –> Frequent Locations and turn it off. However, if you decide to turn it off, your personalized location services settings for Find My IPhone will be automatically restored back if you set your iPhone to lost mode.