Segments can improve throughput by:
Splitting large tables across disks, including tables that are partitioned for parallel query performance
Separating tables and their nonclustered indexes across disks
Placing the text and image page chain on a separate disk from the table itself, where the pointers to the text values are stored
In addition, segments can control space usage, as follows:
A table can never grow larger than its segment allocation; You can use segments to limit table size.
Tables on other segments cannot impinge on the space allocated to objects on another segment.
The threshold manager can monitor space usage.