Short version: your artists, and nothing else about you.
Two things, once you connect it: your top artists and your followed artists. That list becomes your watch list. We do not read your playlists, your listening history, your saved tracks, or anything you have shared with anyone.
Your email address and the fact that Google has verified it. That is what proves the inbox we send alerts to is yours. We do not read your mail.
Your city, if you set one, so alerts can be ordered by what is actually near you. Your notification preferences. That is the whole list.
Announcements, presales, on-sale dates and status changes for the artists on your watch list. How we see them first is the part we keep to ourselves — it is the only real advantage a service this small has. What we will commit to is the outcome: once your artist announces publicly, you hear about it the same day.
The full detail lives in the privacy policy. Disconnect and delete are in your account settings and take effect immediately.