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** <br>
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).<br>
This tactic could be used even on battlefield for quick makeshift charge defense or other defensive maneuvers.

**Military engineering**<br>
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**<br>
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**<br>
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 their crew.