Because it forces the customer table must be selected. Thus, in the book will select just one table and if the customer has more than the number of seats reserved table. It will keep the system out of whack.
It requires customers to select the table. So in the book that will be only a single table. If customers book more than the number of seats of the table. It will cause the system to go haywire
Because it forces the customer to choose the table. So in the book in order to choose one. And if customers who have more than the number of seats of the table, it will make the system malfunctions.