Apple started explaining about your app. use of the IDFA (Advertising Identifier) on app. submission.
I am using Google Conversion Tracking SDK upon my client request. Which requires to add Adsupport.framework to the project Build Phases in xCode. Adsupport.framework uses the IDFA.
On App. submission you will be asked the following:
This app uses the Advertising Identifier to (select all that apply):
1. Serve advertisements within the app
2. Attribute this app installation to a previously served advertisement
3. Attribute an action taken within this app to a previously served advertisement
If you think you have another acceptable use for the Advertising Identifier, contact us.
You must to check at least one of them to be allowed to submit your app.
I don't serve ads on my app. What should I check and why?
You should check the second box. You are using the conversion tracker indicating that you are attributing the app installation to a perviously served advertisement.
来源：https://stackoverflow.com/questions/25251385/idfa-google-conversion-tracking-sdk