This was important at the time. AOL's ad inventory converted VERY well and it was very strategic to keep it out of the hands of Microsoft/Bing and Yahoo, both of whom were serious competitors (on hindsight this was where they were actually beginning to diverge and hit their maxima). In the two sided ads marketplace this was critical to have the most and the highest-quality inventory to bring more network effects w/ advertisers getting good results. The investment was terrible but I suppose they just wrote it down as a $1b fee to keep Yahoo off of AOL.