There is too little known about how microbes in the digestive system affect health. There is at least anecdotal evidence that replacing the microbes in the gut some health problems can be eliminated. It's obvious that far more research on that is needed.
Some years ago I was prescribed an antibiotic for a bladder infection. After taking it, I had a problem with mild intermittent diarrhea for about a month; that is a known problem with some antibiotics. The problem occurs because antibiotics can change the mix of microbes in the gut.