Effects of twisted pair in 120V AC
There is no electrical reason for the twist; it merely serves to keep the two wires physically associated with each other once the Romex jacket is removed. It both &quot;looks neater&quot; and is easier to do subsequent work on.
There is no increased capacitance (the distance between the wires doesn't change), except for the fact that the twisted wires need to be slightly longer than the untwisted wires.
Also, even if there were some increase in reactive current, this would have no effect on an AFCI (which is looking for high-frequency noise) or GFCI (which is looking for a current imbalance between the two wires).
Note that excess capacitance between hot and ground (not neutral) can pass enough current to trip a GFCI. I've seen some kinds of plug-in power line filters do this.