Some PCB manufacturers, such as Eurocircuits or PCBWay, offer the choice of no conductor finish (vs ENIG, HASL, Immersion Tin, OSP or others).
Since this option is not often chosen, it raises the price of small orders since the manufacturer cannot pool multiple orders.
In which conditions would this option make sense?
Could it be for a custom user-applied finish?
Could it be for situations where the surface finish would unpredictably augment the surface roughness, raising the line losses and raising the effective dielectric constant? This does not make sense since the copper will oxidize.