I've always been a sub, so the roles for me are submissive. Some dress up as a female or hospital gown adds to the experience some. I think it's just the idea that it isn't just an enema, there is something else involved. For just an enema it's preparation, insert, flow and evacuate (PIFE). When I've gotten just an enema from someone, it's strip down and PIFE.
When dressed in fem clothes, it was pull down the panty, pantyhose, on all fours and then the PIFE sequence. Being clothed can add to the excitement and danger of an accident, can't make an easy run to the toilet with pantyhose around your calves. Same with a hospital gown, have to gather it up. Have also worn a teddy and nightgowns. For me they were definitely a turn on.
Even in the past being solo I would sometimes don female clothing to role play alone as a female. Other times it was the doctor/nurse/patient fantasy playing out or the 'bitch' that needed to be punished scenario. I believe a lot of dome/sub meetings (normally paid for and can involve enemas) are basically role play anyway unless it's a full time life style.