When I was in boarding school, we had to stand when the master entered the classroom. Then he would say, "Please be seated." It's just more genteel and polite than "Please sit down."
Please be seated is more formal, and it makes the person feel more at ease and welcoming. Please sit down makes someone feel like they're in trouble or something. It kinda makes me think of my teacher, or when I walk into my boss' office.
RE:
What is the difference between "please be seated " and "Please sit down"?
Tell me the difference between "please be seated " and "Please sit down"!!!
I think "please be seated" usually refers to a large seating area. Like in a theater, you say "please be seated" just to tell them to be in a sitting position. "Please sit down" is something you usually say to a person like a guest, when you want them to sit down. It usually refers to just one or a few seats.
That's the best explanation I can give. Honestly, I'm not really sure about the answer either.
"Please be seated" is really formal and more polite than "Please sit down". "Please sit down" is used more on friends and "Please be seated" is used on customers.