The workflow is usually to sculpt out your 3D model, whether it be a gun or a human, make a lower quality model out of the sculpture with the modeling capabilites Blender has, rig, animate, and then texture your asset. The use of modeling a rough 3D model of the sculpture is to reduce the amount of polygons of the asset to increase game frame rate while at the same time keeping all the main details. This is how you would optimize game models. This is called retopology. This is also detrimental to the texturing of the model, which is another feature Blender has. It can texture/paint your model. This is how you create an optimized game asset. Though, some assets, such as rocks, can obviously be made without rigging and animating since they are inanimate objects.