Look up the 'Dead Man's Curve' for a helicopter. It gives the zones for safe flying (in event of engine failure) as a function of speed and altitude. Hover is the left-side of the curve (where V=0).

Very low, a helicopter can safely hover and have an engine failure -- from low altitude, it won't pick up enough speed to have terrible consequences when it reaches the ground.

Up high, a helicopter has enough altitude to use that potential energy to safely autorotate.

There is a region of altitudes in-between where the helicopter can not safely hover in the event of an engine failure.

Look up the 'Dead Man's Curve' for a helicopter. It gives the zones for safe flying (in event of engine failure) as a function of speed and altitude. Hover is the left-side of the curve (where V=0).

Very low, a helicopter can safely hover and have an engine failure -- from low altitude, it won't pick up enough speed to have terrible consequences when it reaches the ground.

Up high, a helicopter has enough altitude to use that potential energy to safely autorotate.

There is a region of altitudes in-between where the helicopter can not safely hover in the event of an engine failure.