Wire shielding is used to protect signal wires. 429 data bus twisted pairs, sensor outputs, co-ax communication wires.....
Shielding keeps outside inductance from close proximity wires from interfering with those shielded signals.
Shielding is normally grounded one one/both ends. Induced inductance is routed to ground.
The use of shielding is strictly an engineering function. I know of no prohibited reasons. Shielded wires add weight to the aircraft, which would be the driving reason of whether to use it or not.
