The view frustrum is a pyramid created from the frustum position and the edges of the viewport. This method sets the distance for the far end of that pyramid. Different applications need different values: e.g. a flight sim needs a much further far clipping plane than a first-person shooter. An important point here is that the larger the ratio between near and far clipping planes, the lower the accuracy of the Z-buffer used to depth-cue pixels. This is because the Z-range is limited to the size of the Z buffer (16 or 32-bit) and the max values must be spread over the gap between near and far clip planes. As it happens, you can affect the accuracy far more by altering the near distance rather than the far distance, but keep this in mind.
far The distance to the far clipping plane from the frustum in world coordinates.If you specify 0, this means an infinite view distance which is useful especially when projecting shadows; but be careful not to use a near distance too close.