Emission Advanced Settings
Emission Glow Noise
This settings adds some variance to the emission texture so its animated and fades in certain areas. A good example is for an impact effect it gives off the effect of embers varying in intensity across the surface.
Emission BG Add
This is for if you want to add more opacity/color to the BG of the glow noise/emission, normally with glow noise its 0-1 but adding the BG allows you to adjust it to say for example 0.5-1 making the black have 50% of the color making it 50% brighter.
Similar to how a SDF works this setting allows you to control the midpoint used for the emission texture. For example lets say you have a gradient that goes from 0-1 in a radial fashion this slider lets you adjust the cutoff range so you can have the circle cut off at 0 or subtract from the texture to have the cutoff at 0.75 making the circle smaller.