I mean if you sum all the currents in all the conductors in a cable/conduit... eg, phase might be carrying 5A, but neutral is carrying 5A in the opposite direction to phase, so if you put a clamp meter on both you'd get 0A because they cancel / sum to zero, if the phase and neutral take different routes then the contents of the indivual cables/ conduits won't sum to zero, which can cause problems with interference to electronic devices, and if a group of conductors which don't sum to zero are totaly surrounded by metal (metal conduit, or metal holes in boxes*) then it can cause issues with eddy currents as it forms an unintentional shorted transformer... (though with a small lighting load the currents involved probably arn't going to be high enough to warm it noticeably...)
*A quick solution to if say phase and neutral have to enter a metal board through separate holes due to physical reasons, would be to cut a small slot between them, and the cables arn't indivudally surrounded by metal; the two holes are effectivly one hole surrounding both cables now
Sorry if this sounds patronising or anything, thats certainly not the way it was intended, I'm most certainly not the best person at getting a point across in an elegant way
*A quick solution to if say phase and neutral have to enter a metal board through separate holes due to physical reasons, would be to cut a small slot between them, and the cables arn't indivudally surrounded by metal; the two holes are effectivly one hole surrounding both cables now
Sorry if this sounds patronising or anything, thats certainly not the way it was intended, I'm most certainly not the best person at getting a point across in an elegant way