Automation saves us a ton of time testing repetitive scenarios. Also, we speed up our testing by setting up some of the scenarios we will need to test a particular project before it is handed off to us from IT.
One point that I keep hearing is that people are no longer motivated to execute each time the same scenario. We have frequent releases for which a whole set of regression scenarios must be executed. Automating these regression scenarios prevents that people get in a routine job.
So while it might be expensive, keeping testers motivated is a big advantage of automation for us.