In my own opinion – personalization, and localization. Also if you have your data, you can store it at Google.See also my previous post, "Google expands personalization".
Google's ambition to organize the worlds information, this is really where it's going.
For more on local search, see also a couple of my previous posts -- "Local search is hard" and "Newspapers should own local". Don't miss the comments by former Director of Yahoo Local Ali Diab on the first of those posts.
For more on storing all your data at Google, see Philipp Lenssen's post, "Google Gdrive Client Leaked", and my post, "In a world with infinite storage, bandwidth, and CPU power".