It seems to me that the most significant, and perhaps reliable, collection of anecdotal evidence lies within the pages of this forum. To the extent that members are reasonably honest in their own accounts and experiences, one would likely never find a more broad based account of enema use and experiences.
When coupled with the plethora of documented, or medical text based information available in Google Books, or other resources, one might be able to make some reasonably informed decisions or suggestions, regarding enema use. Solutions, frequency, positions, and equipment are covered quite extensively.
While many utilize an enema with almost daily frequency, others may actually restrict their use to weekly. Even others may choose a monthly cleanse or only use them with a seasonal change. The wonderful thing is that we each have the choice for ourselves. Those choices may be influenced by our upbringing, personal success or lack thereof, psychological factors, sexual proclivities, or physical limitations.
I've taken, or received enemas, for over 60 years. While I haven't kept a tally on a calendar or in a journal, I've speculated that I've had many thousands of enemas in my lifetime. All were effective and most were very enjoyable. I've always returned to my "normal" bowel/elimination habits and haven't seemed to suffer any negative medical conditions as a result. I've tried to keep solutions and quantities within reason and have enjoyed most of the different types of equipment available.
I suppose there are those times when I've "binged" and enjoyed daily enemas as well as multiple enema sessions. While I enjoy a daily dose of enema related review and participation here and elsewhere, I often will go for days or even weeks without actually taking or receiving an enema. Those small quickie enemas or injections with a bulb syringe, can hardly be lumped in with a larger volume enema even though they are enemas in their own right.
The point is, I'm sure that the medical professionals of today, would not recommend enemas as a regular treatment of digestive distress or issues. Even in cases of more chronic disease, the enemas are small volume injections of a medicine to be absorbed or retained.
If you enjoy enemas, and feel a need to use them, determine your own recommended frequency, solution, position, and type of equipment. Be safe and sane and enjoy this simple pleasure and procedure for as long and often as you desire. If you're fortunate, or lucky, you may even find someone compatible to share your "hobby", or aphrodisiac with. Whether solo, with a partner, or even in a group setting, enemas can be quite an enjoyable indulgence.