Perforce tracks changes for each workspace specification on the server, and this is how it knows which files to update during a p4 sync. This means that each physical workspace needs to have its own workspace specification to track it's own files. To ensure a unique workspaces for each project across all the slaves we append the hostname of the slave to the end of the workspace name given in the "Workspace (client)" field.
If you do not want the plugin to automatically rename clients for each slave then check this box.