Probiotics are beneficial for everyone. Research indicates 70-90% of your immune system is found in your gut and probiotics help you maintain a balance of healthy bacteria.
In fact, healthy bacteria (also known as flora) are one of your main defense mechanisms to fight bugs and other organisms that can make you ill. For millennia, this immune mechanism was needed for the survival of our species.
Humans lived without the use of refrigeration and didn’t always know enough to practice safe food handling. When your gut is healthy, it keeps any foreign invaders in food from getting into the bloodstream.
It also protects you from airborne viruses and bacteria. If you have a digestive system, and you are a mammal (humans are :)), then probiotics are good for you!