Rubbish Bins on Buffet Tables

At every buffet table here in Budapest (like in the hotels), there is a small rubbish bin on the table. I watched others and if they have any "rubbish" during their meal, they deposit it into the bin on he table. I remember thinking this was odd the first time I came to Budapest. Only applies to buffet meals. I guess it makes sense because you don't have the same kind of wait staff. Hmm don't know.