In the current era when hand-built wheels are a rarity reserved mainly for top-end wheelsets spoke nippers have, no doubt, fallen from favor; but in a time before cheap machine-built wheels we replaced rims for all sorts and sizes of wheels. A bike shop had to keep many different sizes of spokes in stock for everything from 16" wheels to 27" wheels. Inevitably there were gaps in the stock and one had to use a larger spoke than optimum. The nippers (if they were sharp) made quick work of the protruding bits of spoke. If they weren't sharp they were pure torture, at least for my skinny hands. Nowadays I use a small electric angle grinder but I never knew of such a tool in 1973.
Brent