It simply means that some strains will take a stronger feed than others. Its that simple really. You only really know when you grow the strain out. But you just feed ay a higher EC/PPM if necessary, it think its more prevalent in hydroponics mediums.
It's like some strains don't like very much, get close to half strength and the tips burn, kind of a trial and error thing as some strains not that stable and the different phenotypes can act slightly different too. IMHO not enough is better/easier to correct than too much, so I always start low and go by what the plant is telling me it wants/doesn't want.