In a blog post Google explained the acquisition:
Skybox’s satellites will help keep Google Maps accurate with up-to-date imagery. Over time, we also hope that Skybox’s team and technology will be able to help improve Internet access and disaster relief — areas Google has long been interested in.
In addition to the obvious benefits to Google Maps and Google Earth, Skybox’s satellites could be used as a means to provide internet access to locations off the broadband grid. The company already has its Project Loon internet-sharing balloons deployed. Adding satellites to the mix would expand the company’s reach.