Wherever you don't care about rust, or have significant current (or don't care about the heat and voltage drop).
The normal applications for it are connecting grounding cages / planes / etc inside electronic items that have shielded (RF) areas, like old CRT TV sets. They don't see environmental moisture (usually), so no rust worries, and there is no significant current on the connecting straps (unless there is some sort of severe failure in which case that's the least of your worries ).
This is a little before (even) my time, but NPS tubing used to be popular material for use in high-performance applications like motorcycle racing frames. One of the primary reasons was, if a crack developed, it was easily visible.
I suspect as chrome molly steel alloys became stronger(And later, alum extruding techniques), cracks became less of a problem.
I think honestly rust is really the only real concern. Yes Nickel plated steel has more resistance than pure nickel, however because it has more resistance, and because we use resistance welding to weld, you can weld thicker nickel plated steel to combat the fact that it has higher resistance. For example if you can only weld up to 0.15mm pure nickel you can probably do at least 0.2mm nickel plated steel.
I personally use nickel plated steel mostly for lower current applications and sometimes for sense wires and stuff like that. The thinner nickel plated steel is easier to weld because you have almost zero electrode sticking compared to pure nickel which can be very sticky and actually eats up electrodes much faster.
I use pure nickel for all higher current applications.