It's not empty space, it's wasted space. Google Plus was brought out as a site to share our stuff, and see what others shared. Now, that's 25% of the real estate. The rest is an invitation to other Google products like Search, Mail and Chat, an incentive to use hangouts, a list of trending topics, a list of unknown people just in case we happen to k ow them, an incentive to invite others to join Google Plus...