It helps you strengthen your fingers in a gradual way, without exaggerated efforts that can hurt you.
As you can regulate the tension individually, you take control of the strength that you want to achieve by gradually increasing the tension, finger by finger. The use of a single finger depends on each one because it requires more effort and can involve anexcessive effort, especially in the little finger.
It is recommended to use groups of fingers. That is, start with four fingers at once and then in groups of three and two (See pictures).