Here are the "uses" for OnStar data on this link - GM has pretty well covered all the bases. Don't doubt if you disconnect the unit and need some warranty work there could be some questions arise from that... it specifically states data is tracked "for warranty administration and validation"
https://www.onstar.com/content/dam/o...statement.html
Didn't have the conversation on break in on my Camaro but when I bought my C7 'Vette I was told that they could track the vehicle data and GM expected customers to adhere to the break in requirements. I did follow those requirements, no doubt they know everything about how you drove the car during that period.