Depends on the wires. But twisting wires together (such as power) minimises loop area for both emission and pickup. So for example from PSU caps to PCB twisting +,- and ground together is good practice.
It reduces the magnetic coupling to nearby circuits/cables, as the fields are much more limited in extent than ad-hoc wire arrangements, and tend to cancel out. It also keeps things tidy.
Basically for any high current wiring you should twist. For signal wiring (high impedance) often shielding is more important to limit capacitive coupling, and twisting not so important, but for low impedance signals (old telephone lines for instance) twisting is essential to keep interference and crosstalk under control in long cable runs.
Ethernet CAT5/CAT6 cable uses four twisted pairs to allow it to operate reliably, and the twist rates are different in the each of the four pairs to further reduce coupling between the pairs.
If you're using differential signals - ie a balanced amp, it actually better if both signal wires are close together as they pass near any noise coupling component. That way the noise coupling is closer to being identical and therefore removed as common signal.