Afaik there is no record of this priviledge being ever invoked, but we only have very scarce information about it so no wonder. Of all named people Shigi Qutuqu might possibly used it when he fucked up the battle against Khwarezmians which didn't resulted in any visible consequence to him, but Genghis might just forgive him without it anyway considering their relations. Also it was him who probably wrote our main source about those event so he might just forgot to mention it (though he did mentioned pretty many embarassing things about Genghis himself).
I feel like "one get out of jail free card, because I like and trust you" is indistinguishable in function from "he forgave him for his failure, because he liked and trusted him otherwise."
Afaik there is no record of this priviledge being ever invoked, but we only have very scarce information about it so no wonder. Of all named people Shigi Qutuqu might possibly used it when he fucked up the battle against Khwarezmians which didn't resulted in any visible consequence to him, but Genghis might just forgive him without it anyway considering their relations. Also it was him who probably wrote our main source about those event so he might just forgot to mention it (though he did mentioned pretty many embarassing things about Genghis himself).
I feel like "one get out of jail free card, because I like and trust you" is indistinguishable in function from "he forgave him for his failure, because he liked and trusted him otherwise."
At least in case of Genghis Khan it functioned the same because He Was The Law.