Gut bacterial are beneficial and have a variety of uses. They assist with breaking down foods, protection from ingested pathogens and manufacturing vitamins and neurotransmitters.
Probiotics are not for everyone. In fact, recent journal articles suggest that they can be a detriment after antibiotic treatment by slowing the return of you normal flora by 6 months.
As far as identifying ideal probiotics for individuals, fecal samples have also been found to be unreliable. I don’t discount that probiotics have some good effects, but it would probably be more prudent to spend your resources healing the gut and addressing the underlying cause of why you needed an antibiotic in the first place.
Check out the source journal article: