Think about what goes on in the electrolytic refining process. We want the impure metal to get oxidized and go into the solution as an ion and then get reduced at the other electrode. In cells (both Daniel and electrolytic) anode ⟹ oxidation and cathode ⟹ reduction. Hence, impure metal (blister copper) is used as the anode. Some precious metals like gold, silver and platinum get deposited below the anode as 'anode mud.'