I've never done it for a living, but Bert's empirical experience is supported by the mathematics, the speed of the hammer head is more important than the weight. Similarly when hitting a minimally compressible material (rock) via an elastic intermediate, (steel drill) a significant portion of the KE will be transferred to the rebound, minimising the effort required to lift the hammer for the next blow. Both are minimised if you simply allow the hammer to drop. So, in 'throwing' the hammer, you are not only more effective, but, providing you time the "throw" correctly as Bert notes, you use less energy not more.
And as Dick notes, if you are driving horizontally you don't have a choice.