The main benefit I see is being able to more accurately represent different light sources. This applies to transmission but also reflectance.
sRGB and P3, what most displays show, by definition use the D65 illuminant, which approximates "midday sunlight in northern europe." So, when you render something indoors, either you are changing the RGB of the materials or the emissive RGB of the light source, or tonemapping the result, all of which can approximate other light sources to some extent. Spectral rendering allows you to better approximate these other light sources.
sRGB and P3, what most displays show, by definition use the D65 illuminant, which approximates "midday sunlight in northern europe." So, when you render something indoors, either you are changing the RGB of the materials or the emissive RGB of the light source, or tonemapping the result, all of which can approximate other light sources to some extent. Spectral rendering allows you to better approximate these other light sources.