Guest IDs are very long, and appear shortened (only the first four digits) in the webclient for staffing. You can also give guests nicknames by editing the guest ID in the webclient.
They're that long in order to be in good compliance with XMPP (Jabber chat protocol) standards. This means that widgets have to do less negotiation with the server when a chat begins, which means that widget chats start up very quickly. And that means a better chat experience for your patrons.