Can Google Contacts store mailing addresses?
Yes. Google Contacts supports street-address fields as part of a contact record, alongside names, email addresses, phone numbers, and other information.
Can I import and export Google Contacts?
Yes. Google provides import, export, backup, and restore tools for contacts.
Why use OnceAsk if I already have Google Contacts?
OnceAsk is focused on the mailing-address workflow: identifying missing addresses, asking the person directly, and maintaining a current address relationship over time. It does not need to replace a general-purpose contacts app.