Probiotics are often unnecessary. A healthy microbiome can be fostered by eating plenty of fresh fruits, vegetables, and fermented foods (yogurt, kefir, etc). There's lots of beneficial bacteria in the environment on the outside of fruit and vegetable for example. High fiber diets also make the environment in your gut better for these microbes so they're more likely to stick around.

I think that probiotics are great but are no replacement for a balanced diet with plenty of fresh fruits and vegetables.