Getting a complete and accurate census count is critically important. That's why your response is required by law. If you do not respond, the U.S. Census Bureau will follow up in person to collect your response.
Why is the census so important? The results are used to determine how much funding local communities receive for key public services and how many seats each state gets in Congress. State and local officials also use census counts to draw boundaries for congressional, state legislative, and school districts.