It is important to check the air pressure of your tyres often. During the winter, it might be that you need to top up your tyres with air, as the pressure drops with decreasing temperatures.
Low air pressure in the tyres will negatively impact your fuel consumption of your vehicle due to increased rolling resistance. It also increases the tyre wear, which means you need to replace the tyres more often. Your car will also not perform as well as it should, if the tyres are not having the correct tyre pressure. This is regardless if you have summer or winter tyres mounted on your car.