Completing a fitness assessment before starting a program is significant as it helps identify an individual's current fitness level, strengths, and weaknesses. This information is crucial for tailoring a personalized training regimen that aligns with their specific goals and capabilities. Assessments can establish baseline metrics such as endurance, strength, flexibility, and body composition, providing measurable targets for progress. Additionally, assessments can identify any underlying health issues that may need addressing before beginning a workout program, ensuring safety and effectiveness.