Saccharomyces boulardii is unique because it is a yeast that is a form of the bakers yeast, but it works differently than most yeast. It is not a cause of a Candida infection, but is instead used to help treat Candida as it is a probiotic.
According to the NIH there are many conditions that it is effective for, particularly in your stomach, the treatment works well for ulcers, and diarrhea http://www.nlm.nih.gov/medlineplus/druginfo/natural/332.html. There is also evidence that it is effective for Crohn’s disease.
A real problem with using Saccharomyces boulardii for yeast infection lies in the fact that it is a fungus. If you take Saccharomyces boulardii with an antifungal, it may reduce the effectiveness of Saccharomyces boulardii making it ineffective.
Saccharomyces boulardii may work better with natural antifungals, and help in strengthening your immune system instead. Combining it with diet, other probiotics, and antifungals would lead to far better results.