Once you turn on unconstrained delegation to a computer, any time an account connects to that computer for any reason, their ticket (TGT) is stored in memory so it can be used later by the computer for impersonation. Let's say you enable this option on a computer you have administrative access to and then get a Domain Admin user to access the computer over the Common Internet File System (CIFS) by accessing a shared folder. Without unconstrained delegation on, only the ticket-granting server (TGS) would be stored in memory on your compromised machine. This ticket gives access only to the CIFS service on your machine so you can't use it to move laterally. However, with unconstrained delegation enabled, when the privileged user connects to your machine, their TGT will stored in memory, which can be replayed to move laterally and compromise a domain controller.