Whenever you use a Google product, such as your Android phone, an Assistant-enabled speaker, or even Chrome, your activity history is stored on the company's servers, and available for you to review through the My Activity service. I personally check it out to understand why my so-called "smart" speaker gave me a meaningless answer by actually reviewing what it thought it heard. My Activity also saves what apps you've used on a given day or what places you've checked on Maps. Because all of this data is private and sensitive, Google just added an extra layer of security to make sure only you can access it.