Ions mean there's some positive electric charge. When you move some ions to one side of membrane, you have charge imbalance. When you have a charge imbalance be

Ions mean there's some positive electric charge. When you move some ions to one side of membrane, you have charge imbalance. When you have a charge imbalance between two sides of some insulator (cellular membrane), you have voltage potential. You can use that potential to do work (like light a diode, turn a motor or do some calculations).