While the use of gold is arguable, I would suggest something more readily convertible to supplies or directly useful such as cattle or iron, it definitely has its uses to turn a body into something solid.
Fast fortifications
Who said the bodies need to be converted at the place they died? You can build castle-like fortifications super-fast and cheap from bodies. If you are evil, friendly bodies will do, either already dead civilian populace from old age/disease or drafted for "building fortifications" (not disclosing the real meaning).
This tactic could be used even on battlefield for quick makeshift charge defense or other defensive maneuvers.
Military engineering
The building potential of readily movable solid material is not limited to fortifications. Enemy burned bridges? Build new one within minutes from their bodies!
Artillery
Assuming same process would work for other living creatures, birds more specifically, you could mount powerful artillery strike against enemy positions even in pre-gunpowder era. Either mass released or trained birds (=smart bombs) killed by Midas arrows or some kind of timed mechanism would turn into deadly projectiles.
Naval combat
Few tons of solid gold on board of enemy ships? Sounds quite powerful. Either delivered from your board and converted later or turning part of thetheir crew using arrows.