This command is needed for interoperability with the OOXML standard and its attribute "arcTo", see ISO/IEC 29500-1:2016 section 20.1.9.4. With the current commands A, B, U, T, V and W only one direction of the arc is possible, either clockwise or counter-clockwise. The new command G allows to specify the arc direction depending on a parameter. Such parameter can be calculated from a formula or adjustment value, so the direction is not predefined.