What exactly is outbound ssh? How to use it and what are the benefits of having it?
That would be ssh traffic originating from your site and connecting to other sites.
You would use it to securely connect to those sites, generally for interactive shell login but possibly also for file transfer, batch-style commands, or port forwarding/tunneling.
This is opposed to inbound ssh, where someone (you at home, or your customers, or whatever) would connect to a service you run.
You might block it if you want to strongly restrict what people can do from your network.