There are three rewards to fasting and prayer. The first one is Greater power in prayer, when the disciples asked Jesus, why can we not cast that demon out. His response to them was, this kind comes with much prayer and fasting. There are times when we need to spend that time in fasting and prayer to se God work in our prayers.
Second, is protection from our enemies. In Ezra he and the people that were with him went to fast and pray for protection from their enemies, and God answered by protecting them!
Third, Guidance for the future. When we are not sure what direction to go, it’s always good to fast and pray for God to show us which way to go and do what we need to do.