What the Google button hands over
It typically shares your address, your name and your profile picture, and it does not share your password or your mail. What it does create is a durable link between the service and your Google identity, and that link keeps existing after you stop using the service.
The button is convenient and the trade is real. Most descriptions of it are either alarmist or silent, and the useful version is short.
On this page
What crosses over at the click
The standard set is an identifier, an e-mail address, a display name and a picture. Your password never leaves Google, and neither does your mail unless the service explicitly asks for that access and you approve it separately. The consent screen lists what is requested, and it is worth reading once rather than never.
The lasting part is the link
After the click, the service holds a stable identifier tied to your Google account. That identifier survives changing your display name and clearing cookies, which is exactly what makes it convenient. It also means the account cannot be quietly separated from your main identity later.
Convenience against separation
Creating a separate address for a service keeps it apart from everything else you do. Using the button connects it. Neither is wrong, and the choice deserves to be conscious rather than made because one option was a single click and the other was a form.
Revoking it later
The connection can be removed from your Google account settings, and removing it does not delete what the service already holds. Revoking stops future sign-ins; it does not reach backwards. Deleting the account at the service is a separate action with a separate result.
Questions before you start
Does Google see what I do on the service?
Not through the sign-in itself. Google learns that you signed in and when, and not what happened afterwards.
Is the button safer than a password?
For password reuse, yes: there is no new password to leak. For linkage, it is the weaker option, because it ties the account to your main identity.
What if I lose access to the Google account?
You usually lose access to everything signed in through it. This is the practical argument for a separate address on anything you want to keep.
Skip the button entirely and open a chat with no sign-in.
Open chat without login