"When Voice & Audio Activity is off, voice inputs won't be saved to your Google Account, even if you're signed in. Instead, they may only be saved using anonymous identifiers."
Ergo, Google is going to collect your voice data no matter what you do, the only question is whether or not it's connected to your account, where you can manually go in and delete it.
So the question now is, if you opt in and later delete your data, does the data actually get deleted, or just disconnected from your account and left only with "anonymous identifiers"?
I actually had this argument out with a former Googler who expressed with incredible strength how importantly Google addressed deletion of data users said to delete. And so his argument was that if you deleted it from your history, it'd be deleted, but if you turned off your history, you'd have no way of telling them to delete it.
"When Voice & Audio Activity is off, voice inputs won't be saved to your Google Account, even if you're signed in. Instead, they may only be saved using anonymous identifiers."
https://support.google.com/websearch/answer/6030020?p=accoun...
Ergo, Google is going to collect your voice data no matter what you do, the only question is whether or not it's connected to your account, where you can manually go in and delete it.