Without a verification mechanism, anyone can pick up the device that has been logged into using your credentials and can see all the activity.
Users can activate verification mode by visiting
activity.google.com, and clicking on the Manage My Activity verification link. Once you click on the link, you will be able to select the Require Extra Verification option, then you need to save, and feed in the verification password to confirm that the changes are being made by you.
In case, you don’t have the verification mode on, when you visit the website you will be able to view all the Google activity from all your devices and it won’t prompt you to confirm the password.
When the verification is turned on, the user will be required to confirm the identity by entering the password and only then the activity details will be visible. For users who have a shared computer, this will prove very useful.
By visiting the Web and App Activity page, you will be able to explore what all activity is being saved by Google and whether or not it is being auto deleted. Once you are convinced with the settings you can save the changes, if not, you can always change it to your liking.