The value in this slider is used to define the size of shadow depth maps used in RayCasting. Resolution is the primary factor in determining the softness of shadows, but the spot light spread and edge quality also affect the general blur level. The shadow map is defined relative to the cone of the spot light, thus a tightly focused spread creates sharper shadows. For example, a spread of 90 requires a Resolution value twice that of a spread of 45 to match the sharpness of the shadows. Very soft and smooth shadows can be obtained using a value of about 50.
Lower values are also faster and consume less memory.
This parameter is only relevant when light fog shadows are to be computed. The higher the value for this parameter, the better the fog shadow quality. Usually, the default is good enough, but sometimes where there is little detail, such a value can miss important fog shadow features, or produce jittery results. The Min Depth is the world space difference that a point is moved towards a spotlight before shadowing is calculated. The value in this slider is used to correct self shadowing problems in RayCast shadows.