Sharing Google Drive documents from Gmail when sending emails

I was writing an email to a customer, and had created a Google Drive spreadsheet for us to collaborate on, I put a link to the document into the email, intending to share the document with the customer immediately after.

To my surprise when I hit Send a prompt came up asking me if I want to share the linked document with the email recipients. You can choose to have it publicly viewable/editable using the link, or even to add the email’s recipients to the document’s share list (which of course requires them to be using a Google account).