Off the record

Gtalk has a feature called "Off the record".

What this does is once you select this option the chat will not be saved. Nither in your history nor his will this be visible.

What is the use actually not much but once you activate this feature you can tell some secrets to him & be sure that he has no proof .
Altjhough once you activate it he can also comes to know abou it and he can he can cancel it .
But once he does so it will be visivble to you too.