To my knowledge, the only thing you lose is your doorway to targeted ads.
Don't forget the opportunity to use your Google ID and password to log onto other sites so Google can track your online activities more closely and thoroughly.
While Google is unquestionably the most ubiquitous gatherer of online activity information and statistics, they have been straight forward in admitting they are selling your data since their policy was changed around the beginning of the twenty-first century. Facebook, on the other hand, is perhaps the more egregious because they have permitted third parties to mine their user's data with no oversight or control of who collected what or how it was used. I deleted my Facebook account but I still have a Google ID because a group I am associated with is hosted there, but I never send email using that account I log into that account only once or twice a year, and my default search engine is DuckDuckGo.