What information does Google Calendar gather?

After using various calendar clients for my own calendars, I miss the Google Calendar app. I stopped using it because I thought that it could steal information from my events in my own calendars (calDev). Can someone confirm this? In case it does not gather info about my calendars I think I wouldn’t mind to give up some other metadata that they could obtain from my usage of the app, I have Google Play services anyway.

Found here