The idea behind dsh is to take a list of targets (machines you can reach via SSH), and run a command or extended script on all of them at once. This is functionality that's wrapped up in a nice GUI in Apple Remote Desktop; it's deeply powerful and very handy. Supposing you wanted to check the uptime for a bunch of your lab boxes -- manually, you'd have to run around, or SSH to each one and run the 'uptime' command. With dsh, you make your machine list (optionally, loading your SSH public key on the machines ahead of time to avoid password prompts) and run one command:
dsh -Ma uptime
Very handy. The full article isn't online yet, but it's worth seeking out a copy of the magazine if you're interested in automation of enterprise Mac admin tasks.