It is not necessary; the 8-10 gallon storage tank alleviates cold water sandwiching effects that occur in some installations. It is meant for comfort purposes only and is not necessary for correct operation of a recirculation loop.
Recirculation
The process of keeping the hot water supply line warm by circulating water, using a pump, through the water line back to the heat source (i.e. Noritz water heater).Storage tank
A vessel in which a body of water is stored.