Are we useful?

Friction is important for all sports. Without it it becomes really hard to accelerate or deaccelerate. For example a 100m sprinter. It would be great for him if there wasnt any air resistance...

If you are stuck with metal for example you can heat it

Both are acceptable, depending on context. For example: Fishing bait is useful to fisherman. Fishing bait is useful for catching fish.

Friction is useful when you are trying to stop a car, but not useful in the pistons of a car's engine (It makes them less efficient).

Example: TV. Electricity- Heat, light, sound. Useful energy transfers would be electricity- light, sound because that's what your TV actually needs, but electricity- heat would be wasted energy or...