It depends on your existing diet and existing gut microbiome. Your stomach bacteria change in population depending on whether you eat healthy, but if your diet consists of pizzas, cake, coke, and all things fast food your microbiome will be absolutely full of bacteria that feast on that kinda stuff, and said bacteria are not great for your long term health. Probiotics are useful for restoring balance to your stomach microbiome, or stabilizing it if you are on a diet that is high in food that would encourage the development of bad bacteria. For the average person, it won't do anything to benefit them.
Ie, if you aren't already in a situation where you need to improve your gut microbiome, it'll give minimal benefits, if any.