Do wires need covering when plastering?
As I understand, the capping was used to protect cables from being sliced by a plasterer's trowel when wet plastering over them.

For the (nominal) cost of them, I'd use capping if the wall was to be wet plastered. (Plus, though it's not always easy, it does give you a chance to re-cable if that ever becomes required in the future).

If the wall was to be dry lined, I'd just clip the cables to the wall.

According to the wiring "regulations", capping is not sufficiently robust mechanical protection to avoid the need for RCD protection to the circuit.