Float Voltage for Battery and its Charger

Please follow the excerpt regarding battery and its charger from a manual -

"It shall be ensured that the float voltage of the battery is the optimum required to ensure the maximum possible period between topping up with electrolyte, without the need for supplementary charging to restore the battery to its fully charged conditions. It shall not exceed the maximum voltage rating of the equipment being supplied."

Q1. float voltage is voltage required to balance very small discharge. is not it? how the above can be ensured? - 'without the need for supplementary charging" can not be justified.

Regards,

sks