Here we go again. The effects of ammonium ions in an emulsion have been documented, and discussed ad-nauseum here. Ammonium is a silver solvent, and as such changes the growth rate and morphology of halide crystal. The use of ammonium is a short-cut method compared to controlled crystal growth. That being said, it's probably quite sufficient for most home-brew emulsions.
Should you want to explore the role of different halide salts in the precipitation, solubility and effects upon vAg will be revealing. That route is however a 'technical' approach - some prefer the "just because" explanation.
I would be pleased to provide further detail off-list.