This is a common question we get. To be on the safe side, we always recommend shutting off the CO2 when you do not have a keg hooked up. Technically speaking, the components of a kegerator will not allow CO2 passed the coupler when it is not hooked to a keg. However, just in case a gasket or o ring does not make a tight seal, shutting the CO2 off will prevent you from losing your CO2 while you do not have a keg hooked up.