shadow maps are good for uniformly soft shadows - the size of the map equates to the sharpness/softness of the shadow. Many lights with large maps will eat RAM fast. The only drawback is that uniformly soft shadows don't always look right. Shadows tend to be sharper at the point of contact between the caster and the receiver and more diffuse with distance (this assumes the light is not a pure diffuse source) so yes that would be faster but can eat all your ram PDQ.

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