Hi Krishna
temp tables are just another tool for the database developer.
They guarantee that the data (global temp table) or both data and table definition (local temp table) are only available to your current session.
Also, modifying this table doesn't create any logging and - due to the guaranteed single session usage - no locking.
They are just a more lightweight data structure that can be used like a table but lives a "short and easy life" 
.
Hope that makes sense to you.
- Lars