The size category defines the expected space required for the table on the database. It logically assigns your table a class for which a certain amount of space is assigned on the database.

You can choose a size category from 0 to 4 for your table. Each category is assigned a certain fixed memory size on the database, which depends on the database system used. When a table is created, initial space is reserved on the database. If more space is required at a later time due to data entries, additional memory will be added depending on the selected size category.

Selecting the correct size category prevents a large number of very small extents from being created for a table. It also prevents space from being wasted if extents which are too large are created.