How is the electric guitar useful?

It is easier to play due to lower action (distance of the sting from the fretboard). It is versatile and has volume and tone controls (usually). Its can have a tremolo system and it is easy to amplify. Plus they look cool!!!

If you mean "how is the electric guitar useful for life" then i can tell you that playing an instrument makes you brain sharper, gives you a sense of achievement and pride. It can open doors for you and will help you meet new people.

Good luck!