Your patients have no way of knowing when to actually leave home, so they guess (arriving early out of caution, or late out of habit) and get it wrong the moment something genuinely unpredictable happens, like a doctor stepping away or running well behind schedule.
When your patients can see the real status themselves, they stop showing up all at once "just in case." Your waiting room clears as people time their arrival correctly, instead of staying full of people who guessed wrong.
One doctor, one or two staff, any specialty. With just one doctor, it's still your one staff member fielding the same question all day, in a waiting room too small to absorb everyone arriving "just in case."
2–10 doctors under one roof, one location, real walk-in and appointment volume. The same guessing now happens across every doctor at once. More patients, more of your reception's time lost to the same question, doctor after doctor.
Smaller nursing homes up through larger multi-department hospitals. Your OPD has the same patients guessing at when to leave home, just multiplied across far more people, and less space to absorb the crowd it creates.