Roof drains without covers happily swallow leaves, plastic wrappers, small stones and all kinds of debris. These settle inside, form clogs, and suddenly water has nowhere to go during heavy rain. Result: pond on the roof, seepage risk below.
Basic grilles or strainers stop large debris from entering in the first place. Yes, they still need occasional cleaning, but the dirt is easier to remove from the top than from inside the pipe.
Looking for covered drains tells you whether someone has thought practically about roof maintenance or not.
