Using a dehumidifier does help prevent mold and mildew from forming inside an individual's house. By removing moisture, one effectively removes one of the four elements mold needs to grow.
It is recommended to use a dehumidifier with a humidistat, a permanent drain and a timer to control mold and mildew. While a dehumidifier is one of the best ways to control mold and mildew, keeping the air cool also helps lower the moisture in the air. However, using one's air conditioner is not enough by itself, especially during mild parts of the year. One could also heat the house temporarily and then open the windows to let out moisture, which should help control mold and mildew.