A conventional nut made of relatively soft plastic or bone will easily clamp the string and make fine tuning difficult. The clamping effect does not only result from too narrow nut slots, but notably more from the impression of the string windings into the nut material at the bottom of the slot. That effect is more prevalent with wire wound nylon strings than with steel strings.
A standard nut made from soft plastic or bone will readily grip the string and make adjustments hard to achieve. The gripping effect arises not just from too narrow nut openings, but more significantly from the impression of the string coils into the nut material at the bottom of the slots. This phenomenon is more pronounced with nylon strings that have wire windings compared to steel strings.