
As Google notes, “Choosing ‘Keep’ means that you can use existing estimated locations to organize and find photos.” If you choose to delete them, you will get a message that says, “Deleting estimated photo locations based on Location History may result in permanent loss of those estimated locations. Your photos will be kept.”

If you want to, disable Estimate missing locations on your iOS or Android phone
You might have estimated photo locations toggled on by default. To check, open the Google Photos app and tap on the profile picture in the upper right corner of the screen. Tap on Photos settings > Location > Location sources. There is a toggle for “Estimate missing locations.” If it bothers you that Google is using landmarks in your pictures to take an educated guess about where you were, make sure that this setting is toggled off.

You should receive this alert in the Google Photos app on iOS and Android