It's more an interferance effect that can extend the lift coefficient of the plane to higher values than it would otherwise. It's not that the ground effect makes the plane able to fly faster or even allows it to. As such it's not really usable other than at takeoff and landing times.

I've got a wonderfully underpowered bipe that lifts off and then needs to have a few moments to accelerate just off the ground before it will trim to a hands off climb. That's also ground effect in action.