WATCHING OR WAITING
Which is more erotic or humiliating: watching your wife in bed with another man, or waiting at home (or simply away) while she goes off with her lover to have sex? Generally, in a D/s relationship the cuckold has little say in this. The wife will probably be more comfortable with one than the other, and that is what she will choose or she will mix it up if she is open. Sometimes the wife is simply more comfortable not having her husband around at all during her loving making sessions with her lover.
Watching: Seeing sex happen in front of you, and realizing - over and over again - that the woman you see in the throes of passion is your wife, is breathtaking. Even when you engage in sex, you don't get to witness it - seeing a man's penis slide in and out of a vagina is stimulating enough, but when it is your own wife's vagina, it is overwhelming. And watching and hearing orgasms can be tremendously "exciting" for the cuckold to witness! "Exciting" could mean different things to different cucks.
Waiting: On the other hand, if the mind is the most powerful sex organ, there is much to be said for the cuckold who sits at home and masturbates, wondering what his wife and her lover are doing now (and now, and NOW, and...).
Perhaps the most frustrating situation for a cuck is to be placed in chastity and then made to sit at home and wait for the return of his un-faithful wife. Unable to masterbate the cuckolds mind races with thoughts and images of his wife dating, courting and having hot, passionate sex with her lover. With no opportunity to acheive release or to even feel his 'probabley' very hard penis in its chastity device, the "mind screw" taking place is immense.
Your wife/Mistress will determine if you wait or watch. Much of comes down to if she enjoys humiliating & degrading you. If so then by all means she should make cuck watch. They can make you serve them wine, undress them, put his condom on for him, and have you clean them when they finish. However, if her goal is merely to get off with a real man while simply denying you, she may not want the cuck around. It's up to the lovers what role you play if any.