As with just about anything, too much of a good thing may have negative consequences. I take an occasional soapy enema for fun, and quite a few tap water enemas for even more shits and giggles. I have never detected any negative results and have routine physicals that include cardiac, G.I., and urological workups.
In my 62 years of enema use, the numbers must be astronomical. Most here understand that too many is when you start to become aware of some negative outcomes and the results are not positive in any way, shape, or form. Soapy enemas can be harsh and individual tolerances may vary greatly. Most of my reading and research indicates that "gentle" enemas aren't as likely to cause undue issues.
In this day and age, a soapy enema is likely frowned upon by anyone with a medically related certification. They would likely tell you that one is too many. I suspect that anyone in their 70's, 80's, 90's, or even 100's had a strong likelihood of being on the receiving end several times. They must be very fortunate to have survived such harsh, and medically prescribed, indignities.
One of my favorite medical texts by Dr. Benjamin F. Miller, indicated in one chapter that the "enema" seemed to have magical virtues to many of his elderly and senior patients. My mom and grandma likely read that, and other chapters, almost as much as I did.