OK. I will may lose some readers for this as I realize many of you have very firm views on this.....and that's fine with me
Life wouldn't be very interesting if we all thought the same thing about the same things!
I've never experienced or met anyone who was involved in this activity so that already limits my expertise on the subject. However, I have read quite a few blogs and message boards which discuss it. From what I read, there are people who engage in this successfully and it works well for them (in this case I'd define successful as being they view it as an overall positive experience and if they could turn back the hands of time they'd do it again). I have absolutely no problem with this and am happy that they have found something which enriches their lives. I'm all for choice and diversity etc..
In my own personal opinion, I wouldn't like it. While I still viewed myself as being vanilla, I never liked the idea of swinging as I always thought it too dangerous to a relationship to start getting physically involved with others. Obviously lots of people see no problem with this.
I've noticed that many of the blogs and message board postings discussing the activity refer to "gut wrenching" emotions and often pain accompanied by the deepest possible subspace at other times. It appears that in many cases it seems the amount of emotional energy they put into it can take over their lives leading to an unhealthy balance.
I've also read several accounts of where men fantisized about it, enjoyed parts of it when it happened but then later regretted it when their wife started to emotionally bond with the 3rd party and pay less attention to them.
Men and women are different. For men, sex can be another fun activity like playing football and many can easily engage it it with a stranger and have zero emotional involvement. As a broad generalization (to which there are many exceptions, including people reading this) women tend to get more emotionally involved when having sex. If they start having sex with someone over a period of time they're more likely to start bonding with them in some way. This increases the chances of the cuck being somewhat neglected as his wife spends more time with the bull and enjoys new found libido.
I do believe that this has and does work for certain people, but I never could see it working for me personally and my beautiful wife.