Students get used to "their" seats, even in big rooms with lots of empty seats. Makes no sense...but...when I went back to school (as an"older adult" but I don't think a "trashy" one), we always went to the same seats in my geology class. In fact, we had a study group based on sitting at the same table. At the end of the semester, some students said they wished they had sat by us, since we seemed to be having fun, but didn't feel they could change seats and "take someone else's seat." So people DO go to "their" seats.