The function of Steam Turbine Gland Vent condenser as its name implies, is to condense steam, which is usually from a high energy level source. It is supposed to recover steam condensate in steam turbine systems and at the same time recover the latent heat of condensation to heat the feedwater. The economic analysis usually proves it's justification. The cost of an unrecovered steam and the associated energy loss is weighed against the cost of make-up water, which depends on the degree of treatment that is needed in the specific location, and the installed cost of the vent condenser installation. The heat recovery increases the overall plant efficiency which determines the energy savings.
Although condensate recovery is mostly done in the Main Condenser in a power plant (generally for low energy level steam), routing the high energy gland turbine vent to the main condenser is obviously a waste of energy. It would also be an added load to the condenser cooling system, which may turn out to be another water conservation issue.