Set Back of CST

Dear Sir,

I wish to know why a C-form is required to be given by a manufacturer when he can claim the CST amount as set back just like VAT amount?  I mean just like  VAT amount a manufacturer can claim back the CST amount paid by him on his raw materials/inputs purchased which are being used in his production... then what is the importance of the C-form to be given for reduced rate of Tax.  He can pay the full rate of CST and can claim back the same as set back just like VAT know.. Please clarify...

Thanks & Regards,

Venkat