It is good practice to check the pressure of your tires often. Air will slowly leak through the material of the tube / tires naturally and the pressure should be checked often to ensure the pressure is sufficient to not only prevent flat tires but also to ensure proper safety and performance.
Higher pressure, lower volume tires such as road or gravel tires may need to be checked more often than lower pressure, higher volume tires like mountain bike or fat tires. We suggest checking the tire pressure weekly if not daily for some of the narrower higher pressure tires.