All of the apps I build have analytics installed. The reason behind this is so I can collect data related to app usage to help make my apps better. I use a popular analytics service called Flurry Analytics.
Flurry collects data about your device (eg. model number, iOS version) and your app usage (eg. session length, crash reports) but DOES NOT COLLECT ANY PERSONAL INFORMATION. I do not wish to have your personal information. The proof of this is that my apps do not request access to any of your personal information (you would have been prompted if they had), and Apple has done a great job of making sure that without your consent apps cannot access your personal information.
I understand that any data collection about your device or app usage may be unsatisfactory to you. If this is the case, you can opt out. This will opt you out of any app that uses Flurry Analytics – a lot of apps do.