hi prasad;
the assembler arithmatic operators are indeed for simplifying your calculation burdon as Hans has mentioned.they shall be used when you are accessing fixed locations they are a bit like #define in c.
here are a few examples:
a.accessing consecutive fixed address locations:
base_address equ 0a000h
next_address equ base_address+1

mov dptr,#base_address
mov a,#01
movx @dptr,a
mov dptr,#next_address
movx @dptr,a

is same as:
base_address equ 0a000h
mov dptr,#base_address
mov a,#01
movx @dptr,a
mov dptr,#base_address+1
movx @dptr,a

b.accessing an array of structures:
block_length equ 010h
first_loc equ 0h
second_loc equ 02h
block_base equ 0a000h


mov dptr,#(block_base+2*block_length+first_loc
mov a,#02h
movx @dptr,a

above code will put a020h in place of long syntax while assembling and thus access third
element in array of structures.


these are particularly useful while using macros.
Pranav
p.s.did you write an article on linux recently?