I like using gesso because of it's 'shrink' porperties - after globbing on the priming coat, it cures into a nice tight covering that doesn't fill or obscure fine details. This same property sometimes means I have to touch up the priming, but it's simple - I drift past the workbench the next morning, spend 5 minutes dabbing (globbing) at shiny metal spots, and they're ready to paint that evening.
It works a treat on Reaper Bones, too.
Also, I've used white gesso with ink mixed in for a tinted primer. Useful tool!