The best thing about jails is its flexibility, it's ability to be installed on different platforms without much hassle as well as having many options for configuration. It also allows one to setup up all sorts of network configurations like VLANs or private networks as needed. It is easy to manage and has great documentation online making troubleshooting very simple when compared to other similar products out there. We are using FreeBSD jails mainly because we wanted to separate our web applications from our file system so they don't affect our production environment.