The story here is that Google has interwoven its services in such a way that users are logged into them when they log into their account. It is a great strategy considering that some users might not even try a particular service unless it is staring at them on their dashboard. This service just continues that trend. Besides, who does not like coupons?

http://www.pcmag.com/article2/0,2817,2419164,00.asp