Thank you for asking this question. I think it gets to the heart of the issue for many. It seems to me that the answer depends on the people involved. Some people are just into fantasy and more of a hot wife scenario where the husband and wife may have sex but the wife has other lovers. An impotent husband would not work there. I am just not sure that this is cuckolding. The more extreme cuckold is where the husband does not have sex and the wife does not want to have sex with him. In that setting an impotent husband is a plus. It just reinforces the wife's decision and so forth. But the husband still needs to have the mental desire to have sex. I just think the whole thing works better when the cuckold is frustrated, and the wife and lover are satisfied.
I think the most natural and healthy cuckolding relationship is where the husband is frustrated but unable to perform. This could be strictly size or inability to erect or the taking of supplements to make him unable to erect. The cuckold naturally becomes submissive in a setting like that. The wife naturally becomes more dominant and will eventually find men that can be not only sex partners but men that she can respect and look up to. This is helped with the contrast. A white wife with a masculine black man will compare him to an impotent white husband who is tiny. This will go far beyond sex. It may be fantasy for some but it can be achieved if everyone is committed.
The final point I would like to make is that part of this is the respect that a cuckold should have for the man in the relationship. I think that many on this site are really jealous of the real men. What they should develop is respect. If you are impotent or tiny or white and these are things your wife does not respect or desire---that is just reality for you. The pressure is off for you. You do not have to have sex or try to be something you are not. But this should then translate into total respect and gratitude for the man/men who your wife is with.