In principle, the efficiency of a thermal power plant is linked to the temperature difference between the cold and hot sources of the entire thermodynamic cycle. The greater the temperature difference, the higher the theoretical efficiency. The condenser can reduce the efficiency of improving the final temperature.
From a technical point of view, a thermal power plant uses steam to drive a steam turbine to generate work. The temperature of the exhaust steam after the work is completed is still relatively high. and it exists mainly in the form of gas. Steam must circulate continuously to continue doing the job, which requires the job to be completed. If it is not condensed into water through the condenser, the specific volume of waste steam will change significantly during the pump pressurization process, which will consume a lot of labor and also reduce the efeffectiveness.
In short, the purpose of a thermal power plant is to produce electricity and heat. Only by working hard to improve efficiency can you earn more money.