It would make for a stormy relationship where the wife/girlfriend plans sexual encounters with others. It might be an erotic fantasy, but as soon as you have to plan something the eroticism begins to evaporate.
I didn't cuckold but I know its a turn on for my hubby, the reason I know is that a stranger danced with me, both me and hubby had consumed a not to insignificant amount, on the dance floor the stranger hands moved around me in a friendly manner you might say, after that I danced with my husband and he was stiff, so I knew it had an effect.
Back in the room I asked him was he upset about the stranger, he said nothing for a few moments, I could almost hear him thinking and then then pounced on me, I knew he would.
After it was over I said can I now assume that my dance floor adventure turned you on and all he said was, I don't want to talk about it and then went to sleep. let sleeping dogs lie I thought.
The unplanned excursion on the dance floor was erotic but if we had to plan something like cuckolding or hotwifing do, that wouldn't be erotic, somehow there is a difference about spontaneous and planned sex.