A roof that anyone can wander onto—kids, delivery people, random visitors—is a risk. There are edges, tank areas, equipment and sometimes weak parapets.
If roof doors shut properly and, ideally, lock or at least latch, access is controlled. People go up only when necessary, often with permission or supervision. This reduces chances of accidents, mischief, or people using the roof as a secret hangout.
An open, loose door to the roof is a small detail that can invite big problems.
