why we use conversion_exit_alpha_input call function in driver program while creating smartform?

Hi,

     can anyone explain why we use this call function? and can we use other call function instead of this?

CALL FUNCTION 'CONVERSION_EXIT_ALPHA_INPUT'

       EXPORTING

         input  = gv_kostl

       IMPORTING

         output = gv_kostl.

Regards,

Dpk