Address Auto Suggest (powered by Google Places API) allows to fill in shipping/billing address fields conveniently, using only a part of address as a base.
Fewer actions are needed to place an order. Moreover, you have less chance of receiving mistakes from the customer's side, which is also equal to less chance of Cart abandonment and misdirected shipping.
Once a customer starts filling in the first address field, a dropdown with address choices will appear.
The proposed choices are based on a customer's actual location (the closest go first).
Once any of the proposed options is chosen, Country, City, Postcode, Address will be filled with selected data.
For Magento 1:
For Magento 2.1+: