The ability to get logs from all around your network, as well as being able to filter through them for specific events or user accounts.
It's not free but it does have some great features like Alerts so we were happy enough to go without in order to use these other tools at no cost! I'd say this has been my favorite tool of logging our event data over the last few years now though there are many others out there if you want something different (and more expensive). We're solving problems related to security by using Logstorm - allowing us to see what happened when certain things occur within our environment.