You don't have to explicitly re-lease a license. Under standard circumstances, the renewal happens behind the scenes whenever you connect your laptop to the LAN in which the server resides and start QV Desktop. QV Desktop will then silently renew the lease as soon as it has determined by talking to the server that the license assignment is still active.
And there you have the main reason why a lease will always be time limited. How should an administrator in QMC revoke a Named CAL when it has been leased permanently to a laptop that never again comes into view of the server? I don't know about you, but I for my part don't like licenses that "get lost"...