Turning drums & rotors is not a must when replacing shoes or pads. That's a myth, and it'll cost you money and performance.

If a drum or rotor is in bad shape (scored, etc) replace it.

Very few, if any, of the turning machines are capable of turning down a drum or rotor with anything akin to accuracy. Take a rotor off, remount it on the machine, and recut, you'll promptly see what I mean.

Because these machines are inaccurate, they cut unevenly. You get inconsistent thicknesses of the rotor/drum as a result. This creates an effective warpage, and inconsistent flexing of the metal. You lose braking from this, sometimes quite appreciably.

Even if the turning is done accurately, you get a thinner rotor or drum. It can't take the heat saturation as well, and is weaker and more prone to flexing.

Many of the shops set the cut rate far too fast on the machine, giving you a nicely ridged rotor or drum. You lose braking performance and eat up shoes and pads and a result.

With new pads and shoes there can be some bedding in difficulties with previous contamination of the rotor or drum. This can be easily rectified by sanding the rotor or drum. You cannot clean the bedding material in the rotor or drum with a solvent wipe.