If COVID can be spread by those not showing symptoms, how does temperature screening help prevent spread?

Temperature screening is clearly one factor. This is why the Temperature Screening Assistant also offers health survey questions to hone in on other factors that might suggest potential COVID-19 exposure. The CDC has reported that 96% of all hospitalized COVID patients had the combination of fever, cough, and shortness of breath so screening for these three factors has a high probability of locating the most at-risk individuals early.