Cuckholding is a vital part of the relationship if your queen demands that it is. Like AmsDom says, it is the cherry on the cake. It is the ultimate FLR when the guy has no sexual involvement and has to watch another guy pleasure his queen. Imagine the thoughts that go round his head of inadequency, envy, frustration and sadness that it is not him engaging in the act.
It is the utmost feeling of rejection, as you can see it with your own eyes that your queen is loving what is happening to her by another person. You are helpless in preventing this from happening. Also, she is not thinking of you as a dominant, strong sexual being, in her mind you are probably just a small, weak, puny sub.
I think cuckholding really does shift the power to the female and it is the final step for a sub to realise that he is just there to please her in a casual way, just as she could hire a cleaner to clean the house or go to the beauticians. He provides a service to her and that’s all he will ever do. That is crushing to certain males, but I feel that that is the ideal life to service my queen.