Odd as it sounds, it is a real thing, and it really works for some cases.
I haven't heard of it being used at all for chronic constipation. Never. But I'm not an MD. I have heard of it working wonderfully for people who were on long courses of antibiotics that essentially eliminated the good bacteria from their intestines. They ended up with chronic diarrhea, poor absorption, skin problems (sometimes dangerous issues). Sometimes yogurt isn't enough.
I hope I never need it. It's just repulsive.