Comment by Ryan_Jones

I still use Lijit for their "backup ads" feature. Basically, I monitor the CPMs I'm getting from other networks, then set my floor CPM in Lijit to that number. That way, I get about 30% fill with Lijit - but it's guaranteed to be at a higher CPM than the other network. Chaining them together works really well - you just need to do it asynchronously so that it doesn't impact load times.