As someone who works in public health, we use census data on a regular basis to track diseases and make sure there isn’t some new epidemic or outbreak happening. It also allows us to more accurately appropriate resources to addressing health problems.
As stated above, it does get used to gerrymander (redistrict) political wards.
The census bureau has already sent out their really long questionnaire (that goes to like one of every 100 households—I received it and had to complete it under penalty of law). The actual census is a much shorter form (really, it is) and the people only knock on your door if you have NOT completed the document.