Today we’re pleased to announce support in Chrome for an experimental new “autocomplete type” attribute for form fields that allows web developers to unambiguously label text and select fields with common data types such as ‘full-name’ or ‘street-address’. With this attribute, web developers can drive conversions on their sites by marking their forms for auto-completion without changing the user interface or the backend.
Most browsers have auto-complete without having to insert a special tag. Also, what happens when a person has their browser set to not save form field information. Does Google pull it from the person's Google+ profile?
Personally, I do not see the advantage to it unless everyone adopts it. Otherwise it is just one more piece of code to add.