Condoms can be seen in two ways as a barrier: one to prevent the spreading of semen and the other to keep the semen. Plastic pants can be seen as a kind of large condom. They can be very nice in cumplay.
It ads next to the fact that the receptive person not only has cum inside her/his most intimate bodyparts but that she/he is remaining with her/his lower body for some longer time (literally sitting) in the semen of the dominant breeder what makes the powerrelation even more obvious. Having to cum in panties, chastitycage, diaper or plastic pants have also the same metaphorical idea/message as that you (have) to cum in a condom being that you can not are aloud to spread your semen. If you wear a barier as a receptive person after that you have been seeded as a fertility cup or menstruationcup that keeps the sperm of your lover in you it enhances also your motivation and being possesed by his action, semen and DNA. For a man it could be with a buttplug. For man or woman it can be done with a diaper or plastic pants. The fact that semen drips out of you is something that you can not control and has on its own a certain powerdynamic next to the fact that you have been fucked and have received the semen and in a way the signature of your lover in you. Then sitting in this semen has also an extra powerdynamic and can also be nice to play in as masturbate of for example rub your wife's genital and holes with the semen of her lover in plastic pants or being obliged to pull on plastic pants that have been filled with the leaking semen out of your wife of the bull and being obliged to masturbate in or being massaged in this semen.