Essentially, you get the Yahoo results, and decorate, filter, reorganise, improve, combine as you wish. So you get the organic results, which you can then innovate upon.
And it has survived the transition from Yahoo-powered search results, to Bing powered search results: http://searchengineland.com/yahoo-boss-moves-from-yahoos-ind...
Which means you have API access to the second most-used search engine in the industry. So what better way to voice your discontent with Google by supporting a competitor.
Running a successful search engine is expensive, it needs continuous investment into R&D. That's why Yahoo took a step back and partnered with Bing instead. The level of investment needed just to hold status quo with the existing market runs into billions of dollars a year, something Yahoo baulked at. Microsoft, however, were still strongly inclined to invest that every year.