When you use segments, you must also manage their scope—the number of database devices to
which each segment points. You can extend or reduce the scope of a segment.
Extending the Scope of Segments
You may need to extend a segment if the database object or objects assigned to the segment run out of space. sp_extendsegment adds database devices to an existing segment.
Reducing the Scope of a Segment
You may need to reduce the scope of a segment if it includes database devices that you want to reserve exclusively for other segments.