Why calculate Refraction distortion （in mode Index of Refraction）Clip？

Development Rendering
1

I noticed there are a clip when distortion vector very small ，Its said“//this will result in a less expensive apply pass since the clipped pixels won’t set stencil to pass”. Dose it necessary？When enable Refraction， if a triangle normal close to camera vector and we set some refraction here，around this area always have a small circle have no refraction.here is the source code in DistortionCommon.ush:

float2 BufferUVDistortion = ViewportUVDistortion * ResolvedView.ViewSizeAndInvSize.xy * ResolvedView.BufferSizeAndInvSize.zw;

//clip if the distortion distance (squared) is too small to be noticed
//this will result in a less expensive apply pass since the clipped pixels won't set stencil to pass
if (TryToClip) //Tips:This Flag set to True in default pipeline（in strate pipeline is about roughness）
{
	clip(dot(BufferUVDistortion, BufferUVDistortion) - .00001);
}

Dose it necessary clip such a small area to improve the performance？

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