Here is a primer on emissive lighting
In this configuration the intent is to cause the lighting to glow as well create a colour bleed as a light bounce. For the bounce to look right the surface the light bounces off must have a reflection value as part of the PBR material else the rendering engine will not know how much energy, intensity, the bounce surface needs to give off. A mirrored surface for example will have a hight reflective surface as compared to a brick or mud type surface.
The other use for emissive is to give off a light balance between the fore and back ground so the the lighting balance contrast does not look flat and can and is usually done as in your material example you have demonstrated.
Here is a demo I did back a bit that makes use of emissive lighting to increase materiel balance with out blowing out the environment GL lighting base.
The effect is best controlled through an instance of the material but the result is the object will have it’s own light level control built into the material with out having to resort or depend on lighting elements. A good example is Fortnite which I suspect uses a lot of self illumination type materials.
So depending on what you want to do emissive is a rather large brush but if you want a glow then the sum RGB will not work right for this type of configuration