Enable conformant OpenGL texture clamp behavior. Enabling this option activates conformant OpenGL texture clamping. "Texture clamping" refers to how texture coordinates are handled when they fall outside the body of the texture. Texture coordinates can be clamped to the edge or within the image.
that "comformant opengl texture clamp behavior" has something to do with the way the graphics are drawn onto your screen, some textures are drawn outside of the viewable screen, "over the edge" and clamp behavior clamps those textures right to the border of your monitor letting none escape.