When food is going to be served in a self-serve buffet, like in schools cafeterias, a square serving tray is the best choice. These are more secure for people to carry with them to the table and also for the people on the table to organize themselves when sitting and placing the trays one besides the other. They are easier to handle and move around with.
A square serving tray is simple to move along the serving platform in any buffet. It has sufficient room for a main course plate, a small salad plate, a dessert plate and a glass. That is all that is required for lunch or dinner for everything fist and you have plenty of room left to move them around a bit for your bread and utensils.
A square serving tray is easier to store than a round tray and takes up a smaller amount space than a rectangular tray. They are easily organized at the time to wash them and also to set them at the beginning of the line for people to take them on the way to the serving line. It is also a good idea to have a couple of them at home just in case you would like to eat before the television set or in bed instead of on the table.