The Harvesting Fingers, are essential to your adventure and progress in Infernium. You can use them to store Light. At the beginning of the adventure you start with only one harvesting finger. As you progress you will get 4 more.
If you try to harvest light but your fingers are already full you will waste the light. Think about the fingers as a bottle and light as water. If you try to pour more water in, it will be wasted.