As per IS 800:2007, maximum permissible deflection in simply supported steel beam other than industrial building is given by 

                                       
    Some of the reason for limiting deflection is:
•    Excessive deflection may create problems for floor or roof drainage.
•    Excessive deflection may lead to crack in the plaster of ceilings & may damage the material attached to or supported by the beam.
•    There may cause undesirable twisting and distortion of connections and connected materials.