Because heat pumps can also produce chill (in addition to heat), this cold water can be utilised to cool the air in your home via ducted air-conditioning.
For your typical residential home it is currently still cheaper to install totally separate floor heating and aircon systems.
For larger buildings, or buildings where there is not much space for services (such as multiple aircon/heat-pump/hot-water units), there is value in combining the floor heating and aircon.