When should twisted pair wires be used?
There are two key advantages to twisted pairs


Reduced inductance \$ L = N^2 \cdot \frac{\mu \cdot Ae}{l}\$ by twisting the wires together you are reducing \$ Ae \$ the enclosed area and so the inductance.
Twisting the wires together means they are close together and so any noise picked up in one conductor should also be picked up in the other. A differential measurement should not see it.


The obvious down-side is cost. You will pay a little more if you buy a twisted pair or you can twist them your self but if you consider your time is not free this is an extra cost too.