Fret Leveling and Re-crowning should be done only when all the frets are in reasonably good condition and can afford some removal of fret material. Sometimes fret leveling requires resetting the action. That usually depends on how much material needs to be removed from the frets when re-crowned. Resetting the action requires deepening the slots on the nut if a significant amount of material has been removed from the frets. When the time comes the instrument does needs a complete re-fret the nut would have to be replaced. It's important to consider at this point, a complete re-fret. Also to be considered is if some frets are beyond re-crowning a complete re-fret should be done.