The ENZ is relevant if there is a low scrimmage kick that is partially blocked / touched by a lineman within the ENZ -- this touching is ignored. Once the ball is clear of the ENZ, if it crosses the ENZ then bounces back into the ENZ and is touched by an R player, then this touching "counts" and the ball can be recovered by K since it is beyond the regular neutral zone.
The ENZ "dissolves" once the kick crosses it, similar to how the FBZ dissolves once the ball leaves the zone.