Banana peels contain phosphorous and potassium, and will break down over time to add those nutrients to the soil around a plant.
Blueberries are particularly fond of organic matter, and require high amounts of rich organic nutrition in their soil. The bushes won't grow or thrive in soil that is poor or alkaline.
Gardeners can turn banana peels directly into the soil around their blueberry plants for a dose of direct nutrition, or add the banana peels to the compost bin for a more balanced dose of vitamins and minerals.