Revoke the prying big eyed activity controls
The data saved in your account helps give you more personalized experiences across all Google services.
Chills up and down my spine. In other words, Google tracks everything you do, and uses that data to predict what you will do next, influence what you think and do, and serve you targeted ads that are designed to convince you to buy stuff.
On a new phone do not turn it on. If you already have, and want out:
Go to Privacy settings -> Activity Controls. You will see a screen full of the kinds of things that Google tracks, along with a pitch on why them tracking this information is good for you.
Turn off Web & App Activity. Google will give you a long message trying to convince you to let them keep tracking you. This does not put an end to Google collecting this data on you. It only pauses the collection. Nor will this delete the data Google has already collected on you. To delete the data Google has already collected in the Web & App Activity category, go to myactivity.google.com.
Repeat for YouTube History.