Pharaoh's dream was the beginning of Yosef's liberation from the Egyptian jail and the precursor of his ascension to leadership. At the end of Parashas Vayeishav, the Midrash Tanchuma distinguishes between Hashem and man in regard to reward and punishment.
Man strikes with a blade and heals with a bandaid.
Hashem, on the other hand, transforms the source of punishment into the actual healing agent. While the dreams were a catalyst for the reversal of his fortune, they were not the only cause. Horav Elchonon Sorotzkin, zl, asserts that dreams played a pivotal role in Yosef's life. His brothers called him the baal ha'chalomos, the dreamer. He had a dream in which his brothers' sheaves in the field bowed down to his.