Unique vs. Blended terrains

I've done what reading there is on the documentaion and some forums, but I'm still having trouble trying to discern the advantages and disadvantages of one over the other. Is there anyone who has used both and understands these aspects of both? Let's put aside any discussion about how to create them and import them. I've got all of that worked out. I'm just having trouble deciding which is better to use in what situations.