There is room in the middle for a centerpiece or food serving dishes. This is the typical table you would find in a banquet hall.
Standard size (18" wide) chairs are used when figuring the maximum count on the table.
To figure how many can fit in a room, divide the room into a grid with 10' by 10' areas. This will accomodate a table with the chairs and allow a walk space of two feet between the adjacent tables.