I find it very useful for one reason: the senationalism around it makes the companies far easier to track and learn about because they frequently pop up in the media thereafter. Typically you're going to get a lot more articles written about you at a $1b valuation than at $200m. There are hundreds upon hundreds of interesting technology companies around the world, most are difficult to learn about initially, or to find at all. The unicorn / billion dollar tag gets them plastered everywhere.