Treatment objective for serial extraction:
Benefits of Serial Extraction 

Serial extraction guides or encourages eruption of permanent teeth in a favorable position.
Reduces malposition of individual teeth.
Avoids loss of labial alveolar bone.
Reduces treatment time when active orthodontic treatment is required. 

Textbook of ORTHODONTICS Sridhar Premkumar
To intercept a developing arch-length deficiency and to reduce or eliminate the need for extensive appliance therapy
Reduce arch-length deficiency
To plan for extensive appliance therapy
To reduce arch-length deficiency & to plan for extensive appliance therapy